Patent Publication Number: US-9403385-B2

Title: Handheld printer

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is divisional of U.S. application Ser. No. 13/689,864, filed Nov. 30, 2013 which is a CIP application PCT/JP2011/54544, filed Feb. 28, 2011, which was not published under PCT article 21(2) in English, the disclosure of which are incorporated herein by reference in its entirety. 
    
    
     BACKGROUND 
     1. Field 
     The present disclosure relates to a handheld printer comprising a power key for turning the power on and off. 
     2. Description of the Related Art 
     One example of an electronic device comprising a plurality of operation keys is a handheld printer, for example. According to such a handheld printer, an arbitrary operation key is surrounded by other operation keys adjacently disposed. 
     Prior arts that prevent mistaken operation of an adjacent operation key when an arbitrary operation key is operated on an electronic device comprising such operation keys are known. According to this prior art, each operation key is designed with a convex surface shape, ensuring that an operator&#39;s finger does not contact any other adjacent operation key when the operator presses an arbitrary operation key with a finger, thereby preventing mistaken operation of the adjacent operation keys. 
     According to a handheld electronic device capable of handheld use, such as a handheld printer, etc., the electronic device generally comprises a power key for turning the power on and off and at least one function key for executing a predetermined function of the handheld electronic device. With such a handheld printer, the size of each key itself tends to be miniaturized to improve the miniaturization of the entire device, and each key tends to be centrally disposed in one location to improve space efficiency. As a result, when the power key and function key are adjacently disposed in particular, the possibility exists that the power of the device will be turned off due to mistaken operation of the power key each time the function key is operated, impeding normal operation. 
     When the prior art is utilized on such a handheld printer, the power key and function key are formed into a convex surface shape. However, in this case, the convex-shaped keys protrude from the device, causing inconveniences with the handheld printer, which demands miniaturization and portability. In particular, in a case where the power key is made convex in shape, concern arises regarding the mistaken operation of the power key by a contacting object, etc., when the device is carried. Thus, it cannot be said that the prior art is a favorable prior art for preventing mistaken operation for a handheld printer wherein the power key and function key are adjacently disposed. 
     SUMMARY 
     It is therefore an object of the present disclosure to provide a handheld printer capable of preventing mistaken operation of a power key and function key adjacently disposed. 
     In order to achieve the above-described object, according to the first aspect, there is provided a handheld printer comprising: a battery power supply; a platen roller configured to feed the print-receiving paper; a thermal line head configured to perform desired printing on the print-receiving paper fed by the platen roller; a device main body comprising a battery storage chamber configured to store the battery power supply; and a battery chamber cover detachably configured to be mounted on the battery storage chamber. 
     According to the handheld printer of the first aspect, the handheld printer comprises a device main body and a battery chamber cover detachable to the battery storage chamber of the device main body. With this arrangement, the battery power supply can be replaceably stored in the battery chamber, making it possible to cover and block the battery storage chamber by engaging the battery chamber cover. 
     In order to achieve the above-described object, according to the second aspect, there is provided a handheld printer comprising: a battery power supply; a platen roller configured to feed the print-receiving paper; a thermal line head configured to perform desired printing on the print-receiving paper fed by the platen roller; a power key for turning the power supply on and off; at least one function key for causing the handheld printer to execute a predetermined function, disposed adjacently to the power key; a first reaction force applying member configured to apply a reaction force in response to a pressing force of the power key; and a second reaction force applying member configured to apply a reaction force in response to a pressing force of the function key, the reaction force by the first reaction force applying member being larger than the reaction force by the second reaction force applying member. 
     The handheld printer according to the second aspect comprises a power key for turning the power on and off, and a function key for executing a predetermined function. First reaction force applying member applies to the power key a reaction force in response to the pressing force of the power key, and second reaction force applying member applies to the function key a reaction force in response to the pressing force of the function key. With this arrangement, a click feel is achieved when the operator presses each key, achieving a favorable feeling of operation. 
     With such a handheld printer, the size of each key itself tends to be miniaturized to improve the miniaturization of the entire device, and each key tends to be centrally disposed in one location to improve space efficiency. As a result, when the operator attempts to press a specific key, the possibility exists that the operator may mistakenly press an adjacent key as well. In particular, when the power key and function key are adjacently disposed, the possibility exists that the power of the device will be turned off due to mistaken operation of the power key each time the function key is operated, impeding normal operation. 
     Here, in the second aspect, the first reaction force applying member is configured to apply a reaction force larger than that of the second reaction force applying member. As a result, to operate the power key, a pressing force that is larger than that when operating the function key is required. With this arrangement, even if the operator mistakenly touches the adjacent power key when pressing the function key, the power key is difficult to press, making it possible to suppress mistaken operation of the power key. As a result, the operator can normally execute the operation without mistakenly turning off the power of the device. On the other hand, when the operator presses the power key, a relatively large force is required, causing the need to press an accurate position to arise and, as a result, a decrease in the possibility of touching the adjacent function key. Thus, it is possible to prevent mistaken operation of the adjacently disposed power key and function key. 
     Further, since the configuration is thus one wherein the size of the reaction force applied to each key is adjusted, it is possible to prevent mistaken operation even with flat-shaped keys in comparison to a case where mistaken operation of adjacent keys is prevented by designing each key with a convex surface shape. Accordingly, this configuration is advantageous in the case of a handheld printer which demands miniaturization and portability. Further, in a case where each key is made convex in shape as described above, while the contact surface area of the key surface and operator finger is significantly decreased, resulting in the concern of a decrease in operability as well as a significant impact on the outer appearance of the device, a resolution can be made according to the second aspect without changing the surface shape of each key, making it possible to eliminate such concern and impact. 
     In order to achieve the above-described object, according to the third aspect, there is provided a handheld printer comprising: a platen roller configured to feed the print-receiving paper; a thermal line head configured to perform desired printing on the print-receiving paper fed by the platen roller; a pair of side chassis members configured to support the platen roller in a rotatable manner and support the thermal line head so that said thermal line head can press against the platen roller; a housing comprising a top cover constituting a device contour upper part and an undercover constituting a device contour lower part; and a chassis assembly comprising the pair of side chassis members, wherein: the housing encloses the chassis assembly; the chassis assembly further comprises an installation part where a screw hole is formed; the top cover comprises a first boss part provided protruding toward the device inside; the undercover comprises a second boss part provided protruding toward the device inside to a position corresponding to the first boss part of the top cover; the chassis assembly, the top cover, and the undercover are assembled to each other by inserting a screw inserted from one of the first boss part and the second boss part through the screw hole of the installation part and connecting the screw to the other the boss part; and a buffering member is provided between at least one of the first boss part and the second boss part and the installation part. 
     The handheld printer according to the third aspect comprises a platen roller, a thermal line head, and a pair of side chassis members that supports these, and a housing comprising a top cover and an undercover. 
     With this arrangement, it is a possible to provide a buffering member between the top cover and undercover and side chassis members for impact absorption, fix the spacing of the side chassis members at the middle position thereof to suppress deformation of the side chassis members caused by the inertia of a heavy object, provide a guide member separate from the housing to the side chassis members to improve the relative positional accuracy of the guide member to the platen roller and thermal line head, and provide a coil spring to the main chassis member provided to the undercover to suppress the variance in the pressing load when the thermal line head presses against the platen roller as a result of that energizing force, for example. 
     The handheld printer according to the third aspect comprises a chassis assembly comprising a platen roller, a thermal line head, and a pair of side chassis members that supports these, and a housing comprising a top cover and an undercover. Then, the chassis assembly, top cover, and undercover are assembled to each other by inserting a screw inserted from either the first boss part provided to the top cover or the second boss part provided to the undercover through the screw hole of the installation part of the chassis assembly and connecting the screw to the other boss part. 
     At this time, according to the third aspect, a buffering part is provided between at least one of the first boss part of the top cover and the second boss part of the undercover, and the installation part of the chassis assembly. With this arrangement, in a case where the handheld printer is subjected to high impact when dropped, etc., it is possible to absorb the impact transmitted from the top cover and the undercover to the chassis assembly by the buffering member. As a result, the occurrence of a defect in the platen roller and thermal line head as a result of impact can be suppressed, making it possible to achieve a handheld printer with high impact resistance when dropped, etc. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view showing the outer appearance configuration of a handheld printer which is an embodiment of the present disclosure. 
         FIG. 2  is a lateral cross-sectional view taken along line II-II in  FIG. 1  showing the internal structure of the handheld printer. 
         FIG. 3  is a block diagram showing the functional configuration of the handheld printer. 
         FIG. 4  is a diagram showing a simplified electrode configuration of the power key and feed key. 
         FIG. 5  is a cross-sectional view taken along line V-V in  FIG. 4 . 
         FIG. 6  is a cross-sectional view taken along line VI-VI in  FIG. 4 . 
         FIGS. 7A and 7B  are diagrams for explaining the advantages achieved by making the pressing forces of the power key and feed key different. 
         FIG. 8  is a flowchart showing the control details related to the operation of the power key and feed key executed by the CPU with the power of the handheld printer in an on state. 
         FIG. 9  is an exploded perspective view showing the internal structure of the handheld printer, as viewed obliquely from the front and above. 
         FIG. 10  is a perspective view showing the detailed structure of the guide member and beam member, as viewed obliquely from above. 
         FIG. 11  is a perspective view showing the detailed structure of the guide member and beam member, as viewed obliquely from below. 
         FIGS. 12A and 12B  are diagrams showing the shapes of the engaging hole and positioning hole. 
         FIG. 13  is a partially enlarged lateral cross-sectional view showing the relative positional relationship of the guide member, platen roller, and thermal line head. 
         FIG. 14  is a perspective view showing the detailed structure of the main chassis member. 
         FIG. 15  is a perspective view showing the detailed structure of the heat sink, as viewed obliquely from below. 
         FIG. 16  is a lateral cross-sectional view of the heat sink showing the structure of the spring receiving part. 
         FIG. 17  is an exploded perspective view of the chassis assembly showing the fixed structure of the side chassis members and main chassis member. 
         FIG. 18  is an exploded perspective view of the chassis assembly showing the fixed structure of the side chassis members and main chassis member. 
         FIG. 19  is an exploded perspective view showing the internal structure of the handheld printer, as viewed obliquely from the rear and above. 
         FIG. 20  is a perspective view showing the detailed structure of the inside of the top cover. 
         FIG. 21  is a cross-sectional view of the handheld printer showing the structure near the first boss part and the second boss part. 
         FIG. 22  is a perspective view showing the battery storage chamber opened with the battery chamber cover removed, viewing the handheld printer obliquely from the rear and above. 
         FIG. 23  is a horizontal cross-sectional view of the handheld printer. 
         FIG. 24  is a perspective view showing the detailed structure of the battery chamber cover, as viewed obliquely from the left and above. 
         FIG. 25  is a perspective view showing the detailed structure of the battery chamber cover, as viewed obliquely from the right and above. 
         FIG. 26  is a flowchart showing the control details related to the operation of the power key and feed key executed by the CPU in a modification where the feed key is prioritized when the keys are simultaneously operated. 
         FIG. 27  is a flowchart showing the control details related to the operation of the power key and feed key executed by the CPU in a modification where the power key is operated by double-clicking. 
         FIG. 28  is an enlarged top view of the main elements, as viewed from direction A in  FIG. 25 . 
         FIG. 29  is a cross-sectional view taken along line B-B′ in  FIG. 28 . 
         FIGS. 30A and 30B  show cross-sectional views taken along lines C-C′ and D-D′ in  FIG. 28 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following describes one embodiment of the present disclosure with reference to accompanying drawings. 
     The outer configuration of a handheld printer  1 , which is one embodiment of the present disclosure, will now be described with reference to  FIG. 1 . In the following, the downward left direction, upward right direction, upward left direction, and downward right direction in  FIG. 1  are respectively described as front, rear, left, and right. 
     The handheld printer  1  prints print data received from an external device  2  (refer to  FIG. 3  described later), such as a PC terminal or handheld telephone for example, on a print-receiving paper S via wired or wireless communication. This handheld printer  1  can be driven by a rechargeable battery  10  (refer to  FIG. 2 , etc., described later) as its power supply, and can be carried to various locations for use. 
     The handheld printer  1  comprises a substantially right-angled parallelepiped shaped housing  100  which constitutes the device contour and is made of a resin material. This housing  100  comprises a top cover  101  constituting an upper part of the device contour, an undercover  102  constituting a lower part of the device contour, and a cover member  103  openably and closeably provided to the upper front side of the top cover  101 . At the time of printing, the print-receiving paper S is inserted into an insertion port  104  formed between the top cover  101  and the cover member  103 . The inserted print-receiving paper S is guided to a pressing part P (refer to  FIG. 2 ) of a platen roller  111  and a thermal line head  112  described later by a guide member  120  provided below the insertion port  104 , and discharged after printing is completed from a discharging exit  107  formed between the cover member  103  and the undercover  102 . 
     The internal structure of the handheld printer  1  will now be described with reference to  FIG. 2 . 
     The platen roller  111  and the thermal line head  112  are provided within the housing  100  of the handheld printer  1 . The platen roller  111  is rotatably supported by a pair of side chassis members  130 L and  130 R (refer to  FIG. 9 , etc., described later) provided in the interior of the housing  101 , and feeds the print-receiving paper S when rotationally driven by a drive motor  11  (refer to  FIG. 3 , etc., described later). The thermal line head  112  is provided on a heat sink  114  comprising a shaft member  113  on a rear end, and this heat sink  114  is supported so that it can rotate around the shaft member  113  by the above described side chassis members  130 L and  130 R. Further, a plurality of coil springs  115  configured to rotate and energize the heat sink  114  that supports the above described thermal line head  112  to the platen roller  111  side is provided to the main chassis member  150  provided to the inner surface of the undercover  102 . With this arrangement, the thermal line head  112  is capable of pressing against the above described platen roller  111 , and thus contacts the platen roller  111  using a predetermined contact pressure during printing, and performs desired printing on the print-receiving paper S inserted therebetween. 
     When regular printing is performed, the print-receiving paper S is inserted into the insertion port  104  with the cover member  103  closed, causing the print-receiving paper S to be fed by the platen roller  111  while guided by the above described guide member  120 , and desired printing is performed by the thermal line head  112 . In a case where a paper jam or the like occurs, the platen roller  111  is released from the thermal line head  112  by opening the cover member  103 , making it possible to easily pull out the paper. 
     A battery storage chamber  105  configured to store the substantially bar-shaped rechargeable battery  10  is provided to the rear side of the housing  100 , and a battery chamber cover  170  is detachably provided to this battery storage chamber  105 . With the battery chamber cover  170  removed, the above described battery storage chamber  105  opens to the rear surface section of the housing  100  (refer to  FIG. 22  described later). 
     The functional configuration of the handheld printer  1  will now be described with reference to  FIG. 3 . 
     The handheld printer  1  comprises a CPU  12 . This CPU  12  performs signal processing in accordance with a program stored in advance in a ROM  14  while utilizing a temporary storage function of an SDRAM  13 , and controls the entire handheld printer  1  accordingly. 
     The CPU  12  is connected to a power supply circuit  15  configured to perform the on/off processing of the power supply of the handheld printer  1 , a motor driving circuit  16  configured to control the drive of the drive motor  11  that drives the platen roller  111 , and a thermal head control circuit  17  configured to control the drive of the thermal line head  112 . 
     The CPU  12  is connected to a paper detection sensor  18 , a feed key  40  for performing a paper feed operation, and a power key  30  for performing a power on/off operation. The CPU  12  detects whether or not the print-receiving paper S has been inserted into the insertion port  104  based on the detection result of the paper detection sensor  18 . Further, when the power key  30  or the feed key  40  is pressed, the CPU  12  executes the processing corresponding to the pressed key. That is, when the feed key  40  is pressed, the CPU  12  outputs a control signal to the above described motor driving circuit  16 , drives the drive motor  11  to rotate the platen roller  111 , and performs feed processing that feeds the print-receiving paper S a predetermined distance. Further, when the power key  30  is pressed with the handheld printer  1  in a power off state, the CPU  12  outputs a control signal to the power supply circuit  15  and performs power-on processing; and when the power key  30  is pressed with the handheld printer in a power on state, the CPU  12  outputs a control signal to the power supply circuit  15  and performs power-off processing. 
     Note that the above described feed key  40  is operated in a case where paper is to be fed in order to start printing from an intermediate position of the print-receiving paper S in the feeding direction, or in a case where the print-receiving paper S of a length in the feeding direction that is longer than a predetermined length is used and the paper is to be discharged after printing ends, for example. 
     Further, the CPU  12  is connected to a USB interface driving circuit  21 , a wireless communication part  22 , and an infrared communication part  23 . The USB interface driving circuit  21  controls the communication performed with the above described external device  2  via a USB cable (not shown) connected to a USB terminal  24  (refer to  FIG. 1 ). Further, the wireless communication part  22  controls the wireless communication performed with the above described external device  2  that is based on a radio wave other than infrared. Further, the infrared communication part  23  controls the infrared communication performed with the above described external device  2 . 
     The communication standards of the above described wireless communication and infrared communication are switched as follows. That is, in a case where the above described power key  30  is pressed in a power off state with the above described feed key  40  pressed, the CPU  12  executes power-on processing and switches the communication standards. Accordingly, in a case where the communication standard is wireless communication, the standard is switched to infrared communication when the above described operation is performed; and in a case where the standard is infrared communication, the standard is switched to wireless communication when the above described operation is performed. 
     With such a configuration, when printing is performed using the handheld printer  1 , the operator enters print data to be printed on the print-receiving paper S and enters a print start instruction using the external device  2 , such as a PC terminal, handheld telephone, or the like. With this arrangement, the print data is sent from the external device  2  to the handheld printer  1  via the above described USB cable, wireless communication, or infrared communication, and printing is performed by the handheld printer  1  based on the print data. 
     With the handheld printer  1  of such a basic configuration as described above, the above described power key  30  and feed key  40  are configured with different pressing forces required for operation. A detailed description follows. 
     The configuration of the power key  30  and the feed key  40  will now be described with reference to  FIG. 4  to  FIG. 6 . 
     As shown in  FIG. 1  previously described, in the handheld printer  1 , the above described power key  30  and feed key  40  are centrally provided to a key operation part  106  provided to the upper left side of the top cover  101 , and are adjacently disposed. As shown in  FIG. 5  and  FIG. 6 , each of the keys  30  and  40  is respectively configured with key panels  31  and  41 , spacers  32  and  42 , key electrodes  34  and  44  connected to grounded GND electrodes  33  and  43  and the CPU  12 , substrates  35  and  45  made of polyethylene terephthalate (PET), static electricity countermeasure layers  36  and  46  formed by silver for use as a static electricity countermeasure, protective films  37  and  47 , and the like, layered in that order from top to bottom. 
     As shown in  FIG. 4 , the above described GND electrodes  33  and  43  are integrally formed in a pattern on the substrates  35  and  45 , surrounding the circumference of the key electrodes  34  and  44 . Further, the key electrodes  34  and  44  are each connected to the CPU  12  by wiring  38  and  48  formed in a pattern on the substrates  35  and  45 . 
     Metal dome members  39  and  49  made of metal and comprising bulging parts  39   a  and  49   a  that bulge in spherical shape toward the side of the key panels  31  and  41  are provided within a space formed by the above described spacers  32  and  42 , in the interior of the above described key panels  31  and  41 . These metal dome members  39  and  49  utilize the retroflexion of each of the bulging parts  39   a  and  49   a  to apply a reaction force in response to the pressing force of each of the keys  30  and  40 . With this arrangement, a click feel is achieved when the operator presses each of the keys  30  and  40 , achieving a favorable feeling of operation. Further, the metal dome members  39  and  49  also play the role of contacts that connect the key electrodes  34  and  44  and the GND electrodes  33  and  43  when each of the keys  30  and  40  is pressed. 
     At this time, as shown in  FIG. 5  and  FIG. 6 , the configuration is designed so that a bulging volume h 1  of the bulging part  39   a  of the metal dome member  39  becomes greater than a bulging volume h 2  of the bulging part  49   a  of the metal dome member  49 . With this arrangement, the metal dome member  39  applies a larger reaction force than the metal dome member  49 , necessitating a larger pressing force for operating the power key  30  than that when operating the feed key  40 . 
     The advantages achieved by the above described configuration will now be described with reference to  FIG. 7 . 
     In the handheld printer  1 , each of the keys  30  and  40  itself is miniaturized to improve the miniaturization of the entire device, and is centrally disposed in one location of the key operation part  106  as previously described in order to improve space efficiency. As a result, as shown in  FIG. 7A , the possibility exists that, when pressing the feed key  40 , a finger F of the operator may mistakenly touch the adjacent power key  30 . At this time, since the operation of the power key  30  requires a larger pressing force than the feed key  40  as previously described, the power key  30  is difficult to press, thereby making it possible to suppress the mistaken operation of the power key  30 . 
     On the other hand, as shown in  FIG. 7B , when the operator presses the power key  30 , the operator needs to press an accurate position using the finger F since a larger force is required compared to the feed key  40 . As a result, the possibility that the adjacent feed key  40  will be touched decreases. In this manner, it is possible to prevent mistaken operation of the adjacently disposed power key  30  and feed key  40 . 
     The control details related to the operation of the power key  30  and the feed key  40  executed by the CPU  12  with the handheld printer  1  in a power on state will now be described with reference to  FIG. 8 . 
     In step S 10 , the CPU  12  determines whether or not the feed key  40  was pressed. In a case where the feed key  40  has not been pressed, the decision is made that the condition is not satisfied and the flow proceeds to step S 20 . In step S 20 , the CPU  12  determines whether or not the power key  30  was pressed. In a case where the power key  30  has not been pressed, the decision is made that the condition is not satisfied and the flow returns to the above described step S 10 . 
     In a case where the feed key  40  was pressed in the above described step S 10 , the decision is made that the condition is satisfied and the flow proceeds to step S 30 . In step S 30 , the CPU  12  determines whether or not the power key  30  was pressed simultaneously along with the feed key  40 . In a case where the power key  30  has not been pressed simultaneously, the decision is made that the condition is not satisfied and the flow proceeds to step S 40  where the CPU  12  outputs a control signal to the motor driving circuit  16 , drives the drive motor  11  to rotate the platen roller  111 , and executes the above described feed processing that feeds the print-receiving paper S a predetermined distance. Then, the flow returns to the above described step S 10 . 
     On the other hand, in a case where the power key  30  was simultaneously pressed in the above described step S 30 , the decision is made that the condition is satisfied and the flow proceeds to step S 50  where the CPU  12  outputs a control signal to the power supply circuit  15  and executes power-off processing that turns the power of the handheld printer  1  off. Note that the CPU  12  determines that the condition is satisfied, proceeds to this step S 50 , and similarly executes power-off processing in a case where the power key  30  was pressed in the above described step S 20  as well. Then, this flowchart ends. 
     With the above control, steps S 10  and S 20  are repeated during the period in which the operator does not operate either the power key  30  or the feed key  40 . At this time, in a case where the power key  30  is singly operated, the decision is made that the condition of step S 20  is satisfied and the flow proceeds to step S 50  where the above described power-off processing is executed. On the other hand, in a case where the feed key  40  is singly operated, the decision is made that the condition of step S 10  is satisfied and the condition of step S 30  is not satisfied, and the flow proceeds to step S 40  where the above described feed processing is executed. 
     Further, in a case where the power key  30  and the feed key  40  are simultaneously operated, the decision is made that the conditions of both step S 10  and step S 30  are satisfied and the flow proceeds to step S 50  where power-off processing is executed without executing feed processing. The reason that the processing of the power key  30  is thus executed with priority is that, in a case where the power key  30  and the feed key  40  are simultaneously pressed under conditions where operation of the power key  30  requires a larger pressing force than the feed key  40  as previously described, a larger pressing force was most likely applied to the power key  30 , making it possible to infer in this case that the operator pressed the keys with the intention of operating the power key  30 . Accordingly, by performing the above described control, it is possible to perform processing conforming to the intention of the operator. 
     Next, the fixed structure of the guide member  120  previously described will be described with reference to  FIG. 9  to  FIG. 13 . Note that each of the front, rear, left, right, up, and down directions in the following description corresponds to each direction with each part, such as the guide member  120 , etc., installed in the handheld printer  1 . 
     As shown in  FIG. 9 , the handheld printer  1  is generally assembled by assembling the top cover  101 , the undercover  102 , and the cover member  103 , which constitute the housing  100 , and the chassis assembly  50 . The chassis assembly  50  comprises a main chassis member  150  that constitutes the bottom part of the chassis assembly  50  provided on the inner surface of the undercover  102 , and the pair of side chassis members  103 L and  130 R that are arranged in a standing condition from both ends of this main chassis member  150  in a longitudinal direction. The side chassis members  130 L and  130 R rotatably support the platen roller  111  with a shaft member  111   a  of the platen roller  111  inserted through a shaft hole  131 . Further, the side chassis members  130 L and  130 R rotatably support the heat sink  114  comprising the thermal line head  112  via the shaft member  113  previously described. 
     The previously described drive motor  11  configured to drive the platen roller  111 , and a gear mechanism  132  made of a plurality of gears and configured to transmit the driving force of this drive motor  11  to the above described shaft member  111   a  of the platen roller  111  are provided to the side chassis member  130 L on the left side. 
     Further, a beam member  140  forms a bridge across and is fixed with screws on the upper part of the side chassis members  130 L and  130 R. Then, the guide member  120  previously described that guides the print-receiving paper S inserted from the insertion port  104  to the pressing part P of the platen roller  111  and the thermal line head  112  is configured as a separate entity separate from the top cover  101 , the undercover  102 , and the cover member  103  that constitute the housing  100 , fixed to the above described beam member  140 , and thus provided to the side chassis members  130 L and  130 R. 
     As shown in  FIG. 10  and  FIG. 11 , the guide member  120  comprises a horizontal surface  121 , which is substantially horizontal when assembled to the chassis assembly  50 , on the upper part thereof, and an inclined surface  122  that inclines from this horizontal surface  121  toward the device interior. A plurality of protruding members  123  formed along the guided direction of the print-receiving paper S is provided in parallel in the longitudinal direction on the horizontal surface  121  and the inclined surface  122 . Further, the guide member  120  comprises rib parts  124  and  125  arranged in a downward standing condition on both sides in the front/rear direction of the lower part of the above described horizontal surface  121 . With these rib parts  124  and  125  and the above described horizontal surface  121 , the lateral cross-sectional shape of the rear side of the guide member  120  substantially forms an upside-down u-shape, and that section is installed so that it covers the beam member  140  (refer to  FIG. 13  described later). 
     Fixing tab members  126  capable of engaging with a plurality (five in this example) of engaging holes  141  provided to corresponding positions on the front side (the left lower side in  FIG. 10 ; the left upper side in  FIG. 11 ), which is one side of the beam member  140  in a width direction, are provided to a plurality of locations (five in this example) of the above described rib part  124  in a longitudinal direction, protruding to the rear side (the right lower side in  FIG. 11 ). These fixing tab members  126  are formed into the same shape. On the other hand, a hook-shaped hook member  127  capable of locking into a locking part  142  provided to a corresponding position on the rear side (the right lower side in  FIG. 11 ), which is the other side of the beam member  140  in a width direction, is provided to one location of the above described rib part  125  in a longitudinal direction. With this arrangement, the guide member  120  can be fixed by locking the hook member  127  into the locking part  142  on the rear side of the beam member  140  with the above described fixing tab members  126  engaged with the engaging holes  141  on the front side of the beam member  140 , and inserting the beam member  140  by the above described fixing tab members  126  and the hook member  127  from both sides in the front/rear direction thereof (refer to  FIG. 13  described later). Note that while the above described locking part  142  and the hook member  127  that locks thereto are provided to one location of the beam member  140  in a longitudinal direction and the guide member  120 , respectively, they may be provided to a plurality of locations. 
     Further, one engaging hole  141  (hereinafter suitably described as the “positioning hole  143 ”) of the above described five engaging holes  141  provided to the beam member  140 , positioned at the center in the longitudinal direction, is formed so that the vertical dimension is smaller than the other engaging holes  141 , as shown in  FIG. 12A  and  FIG. 12B . The vertical dimension of this positioning hole  143  is substantially the same as the vertical dimension of the fixing tab member  126 . With this arrangement, when the fixing tab members  126  of the guide member  120  are engaged with the engaging holes  141  of the beam member  140 , the vertical position of the guide member  120  can be positioned by the above described positioning hole  143 . Note that while here one of the engaging holes  141  is established as the positioning hole  143 , a plurality of the engaging holes  141  may be established as the positioning holes  143 . 
     As shown in  FIG. 13 , the thermal line head  112  comprises an elevated part  116  (refer to  FIG. 9  as well) made of resin for protecting the semiconductor element that drives the heating element, on the surface. Here, a feeding path R of the print-receiving paper S is a path from the insertion port  104 , through the above described inclined surface  122  of the guide member  120  and the pressing part P of the platen roller  111  and the thermal line head  112 , to the discharging exit  107 . That is, the feeding path R is demarcated mainly by the relative positional relationship of the guide member  120  with respect to the platen roller  111  and the thermal line head  112 . Then, the vertical positioning of the guide member  120  by the positioning hole  143  of the above described beam member  140  is set so that the above described feeding path R can stay clear of the above described elevated part  116 . Further, with the guide member  120  fixed to the beam member  140  as previously described, the angle of the inclined surface  122  is set so that the above described feeding path R can stay clear of the elevated part  116 . With this arrangement, it possible to prevent the occurrence of defects caused by the print-receiving paper S contacting the above described elevated part  116  of the thermal line head  112  in the feeding path R, such as the impeding of insertion from the insertion port  104  or paper jams. 
     Next, the energizing structure of the heat sink  114  based on the coil springs  115  provided to the main chassis member  150  will be described with reference to  FIG. 14  to  FIG. 16 . Note that, in  FIG. 14 , a control substrate  60  is shown in phantom to prevent confusion. 
     As shown in the previously described  FIG. 2  and  FIG. 9 , the main chassis member  150  made of metal constituting the bottom part of the chassis assembly  50  is provided to the inner surface of the undercover  102 . As shown in  FIG. 14 , the main chassis member  150  comprises a front rib part  151  having a substantially L-shaped cross-section that bends upward along the longitudinal direction, at the front (upper left side in  FIG. 14 ) end thereof. Further, the main chassis member  150  comprises a rear rib part  152  having a substantially L-shaped cross-section that similarly bends upward along the longitudinal direction, at the rear (lower right side in  FIG. 14 ) end thereof. The above described front rib part  151  is formed by bending the front end of the main chassis member  150  across the longitudinal direction in its entirety, and the above described rear rib part  152  is formed by bending a center section of the rear end of the main chassis member  150  in a longitudinal direction. Further, the vertical length of the front rib part  151  is configured longer than that of the rear rib part  152 . 
     The above described front rib part  151  comprises a first left fixing part  153  fixed to the left side chassis member  130 L, on the left end (right end in  FIG. 14 ), which is one end side in a longitudinal direction; and a first right fixing part  154  fixed to the right side chassis member  130 R, on the right end (left end in  FIG. 14 ), which is the other end side in a longitudinal direction. These fixing parts  153  and  154  are formed by bending both ends of the front rib part  151  in a longitudinal direction rearward along the planar direction of the side chassis members  130 L and  130 R. 
     Further, a second left fixing part  158  used for fixation with the side chassis member  130 L is bent upward and formed at the rear on the left end of the main chassis member  150 , and a hook-shaped second right fixing part  159  used for fixation with the side chassis member  130 R is bent upward and formed at the rear on the right end of the main chassis member  150 . 
     A plurality (three in this example) of coil springs  115  configured to rotate and energize the heat sink  114  to the platen roller  111  side is provided to a plurality of locations (three in this example) in a longitudinal direction near the above described front rib part  151 , on the main chassis member  150 . These coil springs  115  are each supported by insertion through a spring support shaft  155  (refer to  FIG. 2 ) provided in a protruding condition to a corresponding position of the main chassis member  150  so that they are stably arranged in a standing condition. The coil springs  115  are provided at equal intervals in three locations of the main chassis member  150  in a longitudinal direction, and comprise a first coil spring  115 C provided correspondingly to a center position of the thermal line head  112  in a longitudinal direction, and two second coil springs  115 L and  115 R positioned on both left and right sides of this first coil spring  115 C. Note that, in this description, each of the coil springs  115 C,  115 L, and  115 R is described simply as the “coil spring  115 ” when distinction is not required. 
     The spring constant of the first coil spring  115 C is greater than the spring constant of the second coil springs  115 L and  115 R. Since the handheld printer  1  is a printer that feeds and performs printing on the print-receiving paper S using the device center position in a longitudinal direction as standard as indicated by paper alignment position displays M formed on the surface of the top cover  101  (refer to  FIG. 1  and  FIG. 9 ), this difference in spring constants is to ensure that the thermal line head  112  is energized by the first coil spring  115 C having the largest spring constant at the center position in a longitudinal direction which serves as that standard, and energized by the second coil springs  115 L and  115 R having the smaller spring constants on both sides thereof, causing the pressing load of the thermal line head  112  to act with good balance and achieve stability in the longitudinal direction, even if the size of the print-receiving paper S is changed. 
     Further, as shown in  FIG. 2  and  FIG. 14  previously described, in the handheld printer  1 , the control substrate  60  on which electronic devices are mounted is provided between the main chassis member  150  and the heat sink  114  that supports the thermal line head  112 . This control substrate  60  is inserted between the front rib part  151  and the rear rib part  152  previously described, and installed by screws (not shown) to a plurality (three in this example) of installation parts  156  cut and formed from the main chassis member  150 . A plurality (three in this example) of concave parts  61  for inserting the coil springs  115  is provided to positions corresponding to the coil springs  115  on the peripheral edge of this control substrate  60 . 
     As shown in  FIG. 15 , concave-shaped spring receiving parts  117  are provided to positions corresponding to the above described coil springs  115 , on a lower surface  114   a  of the heat sink  114  on the opposite side of the thermal line head  112  side. This spring receiving part  117  comprises at the bottom thereof a contact surface  117   a  configured to contact the upper end of the coil spring  115  and, as shown in  FIG. 16 , is provided so that, even in a case where the posture is such that a planar direction X of the heat sink  114  is not orthogonal to an axial direction Y of the coil spring  115  due to the rotational movement around the shaft member  113 , the above described contact surface  117   a  is substantially orthogonal to the above described axial direction Y. With this arrangement, the upper end of each of the coil springs  115  is caused to contact the above described contact surface  117   a  of the corresponding spring receiving part  117 , making it possible to cause an energizing force to stably act on the heat sink  114 . 
     Further, as shown in  FIG. 16 , the spring receiving part  117  is provided to the front (left side in  FIG. 16 ) end of the heat sink  114 , which is the other end in a width direction. That is, the coil spring  115  is configured so that the heat sink  114  is energized to the platen roller  111  side, further frontward than the position of the pressing part P of the thermal line head  112  and the platen roller  111 . With this arrangement, it is possible to decrease the required energizing force compared to a case where energizing occurs at a middle position of the heat sink  114 , between the rear end and front end, particularly further rearward than the pressing part P, thereby improving miniaturization of the coil spring. 
     Next, the fixed structure of the side chassis members  130  and the main chassis member  150  will be described with reference to  FIG. 17  and  FIG. 18 . Note that, in these  FIGS. 17 and 18 , illustration of the guide member  120  is omitted. 
     As shown in  FIG. 17  and  FIG. 18 , a convex part  133  is provided in two front/rear-direction locations to each of the base ends, which are the lower ends of the side chassis members  130 L and  130 R. These convex parts  133  are formed in order to provide engaging holes  134  described later to the base ends of the side chassis members  130 L and  130 R. Note that these convex parts  133  are each housed within a concave part  108  (refer to  FIG. 9 ) provided on the inner surface of the undercover  102  when the undercover  102  and the chassis assembly  50  are assembled. 
     The engaging hole  134  with which a protruding part  157  provided to both ends of the main chassis member  150  in a longitudinal direction engages is formed on each of the above described convex parts  133  of the side chassis members  130 L and  130 R. With each of the protruding parts  157  engaged with the corresponding engaging hole  134 , the base ends of the side chassis members  130 L and  130 R are positioned at both end positions of the main chassis member  150  in a longitudinal direction. 
     A screw hole  135  through which is inserted one of a plurality (three in this example) of connecting screws  118  is respectively provided to the side chassis members  130 L and  130 R. The screws  118  are inserted through the above described screw holes  135  of the side chassis members  130 L and  130 R, thereby connecting the first left fixing part  153  and the first right fixing part  154  of the above described front rib part  151 , both ends of the above described beam member  140  in a longitudinal direction, and the above described second left fixing part  158  and second right fixing part  159  provided at the rear of the main chassis member  150 . With this arrangement, the side chassis members  130 L and  130 R are fixed to the main chassis member  150 . The chassis assembly  50  thus configured is assembled to the undercover  102  while each of the above described convex parts  133  of the side chassis members  130 L and  130 R is caused to be housed in the above described concave parts  108  of the undercover  102 . 
     As a result, the base ends of the side chassis members  130 L and  130 R are positioned at both end positions of the main chassis member  150  in a longitudinal direction by the protruding parts  157  of the main chassis member  150 , and the left side chassis member  130 L and the right side chassis member  130 R are connected at a middle position between the base ends and the providing part of the platen roller  111  or the thermal line head  112  by the front rib part  151  of the main chassis member  150 . 
     Next, the buffering structure of the chassis assembly  50  of the handheld printer  1  will be described with reference to  FIG. 19  to  FIG. 21 . 
     As shown in  FIG. 20 , first boss parts  161 L and  161 R configured to protrude toward the device inside are provided to the inside of the top cover  101 , at both width-direction ends of the rear side thereof (upper right side in  FIG. 20 ). A screw groove (not shown) is formed on the inner peripheral surface of these first boss parts  161 L and  161 R. On the other hand, as shown in  FIG. 19 , second boss parts  162 L and  162 R configured to slightly protrude toward the device inside are provided to the inside of the undercover  101 , at both width-direction ends of the rear side thereof (lower left side in  FIG. 19 ). 
     Further, as shown in  FIG. 19 , the chassis assembly  50  comprises installation parts  51  and  52  where screw holes  51   a  and  52   a  (refer to  FIG. 21 ) are formed at both width-direction ends of the rear side thereof. The above described installation part  51  is formed by bending the rear side of the base end of the side chassis member  130 L toward the width-direction outside (lower right side in  FIG. 19 ). Further, the above described installation part  52  is integrally provided at the rear on the right side of the main chassis part  150 . A spherical rubber member  53  is provided to each of the upper parts of these installation parts  51  and  52 . 
     The first boss parts  161 L and  161 R of the above described top cover  101 , the installation parts  51  and  52  of the chassis assembly  50 , the rubber members  53  and  53  respectively provided to the upper parts of these installation parts  51  and  52 , and the second boss parts  162 L and  162 R of the undercover  101  are each provided to corresponding positions in the vertical direction. Then, the top cover  101 , the undercover  102 , and the chassis assembly  50  are assembled to each other by inserting the screws (not shown) inserted from the second boss parts  162 L and  162 R of the undercover  102  through the screw holes  51   a  and  52   a  of the installation parts  51  and  52  of the chassis assembly  50  and the rubber members  53  and  53 , and connecting the screws to the first boss parts  161 L and  161 R of the top cover  101 . 
     In this manner, when the top cover  101 , the undercover  102 , and the chassis assembly  50  are assembled, the installation parts  51  and  52  of the chassis assembly  50  are inserted between the first boss parts  161 L and  161 R of the top cover  101  and the second boss parts  162 L and  162 R of the undercover  102 . At this time, for the chassis assembly  50  and the undercover  102 , contact is made at the installation parts  51  and  52  and the second boss parts  162 L and  162 R while the base ends of the side chassis member  130  previously described are not in contact with the inner surface of the undercover  102 . On the other hand, for the chassis assembly  50  and the top cover  101 , only the installation parts  51  and  52  and the first boss parts  161 L and  161 R are indirectly in contact via the rubber member  53  provided therebetween. With this arrangement, the impact transmitted from the top cover  101  to the chassis assembly  50  can be effectively absorbed by the rubber member  53 . 
     Further, the top cover  101  comprises boss support members  163 L and  163 R (only the boss support member  163 R is shown in  FIG. 20 ) configured to support the first boss parts  161 L and  161 R so that the impact transmitted from the cover to the first boss parts  161 L and  161 R can be absorbed. As shown in  FIG. 20 , the boss support member  163 R comprises a standing part  164 R arranged in a standing condition from the upper rear side of the top cover  101  toward the device inside, and a bending part  165 R provided bending from this standing part  164 R, with the first boss part  161 R provided on the above described bending part  165 R. Note that the boss support member  163 L also has the same structure as the above described boss support member  163 R. With such a structure, the boss support members  163 L and  163 R are capable of absorbing the impact transmitted from the top cover  101  to the first boss parts  161 L and  161 R by the flexure that occurs between the standing parts  164 L and  164 R and the bending parts  165 L and  165 R. 
     Further, as shown in  FIG. 20 , the top cover  101  comprises rib parts  166 L and  166 R configured to protrude a predetermined distance further toward the device inside (upper side in  FIG. 20 ) than the tip parts of the first boss parts  161 L and  161 R, around the first boss parts  161 L and  161 R. The above described rib part  166 L is arranged on the width-direction outside of the first boss part  161 L (the right lower side in  FIG. 20 ; the right side in  FIG. 21 ), and the above described rib part  166 R is arranged on the rear side (upper right side in  FIG. 20 ) of the first boss part  161 R. Note that only the rib part  166 L is shown in  FIG. 21  based on the cross-sectional direction. The tips of these rib parts  166 L and  166 R contact the installation parts  51  and  52  of the chassis assembly  50  when the top cover  101 , the undercover  102 , and the chassis assembly  50  are assembled, restricting the movement of the first boss parts  161 L and  161 R toward the installation part  51  and  52  side. With this arrangement, the amount of compression of the rubber member  53  is prevented from becoming excessive, thereby preventing decreases in the buffering function and durability of the rubber member  53 . 
     Next, the structure of the battery chamber cover  170  detachable from the battery storage chamber  105  will be described with reference to  FIG. 22  to  FIG. 25 . 
     As previously described, the battery chamber cover  170  is detachably provided to the battery storage chamber  105  and, as shown in  FIG. 22 , the battery storage chamber  105  configured to store the rechargeable battery  10  opens to the rear surface section of the housing  100  with the battery chamber cover  170  removed. 
     The battery chamber cover  170  comprises at the left end (right end in  FIG. 22  to  FIG. 25 ), which is one end thereof in a longitudinal direction, an upper/lower pair of the locking tabs  171  that fit into a locking hole  109  (refer to  FIG. 23 ) provided to the left end, which is one end in a longitudinal direction, of the battery storage chamber  105 . Further, the battery chamber cover  170  comprises at the right end (left end in  FIG. 22  to  FIG. 25 ), which is the other end in a longitudinal direction, an elastic engaging part  172  that elastically deforms and engages with an engaged part  110  provided to the right end, which is the other end in a longitudinal direction, of the battery storage chamber  105 . When the battery chamber cover  170  is mounted onto the battery storage chamber  105 , the above described locking tabs  171  of the left end are first fit into the above described locking holes  109  of the battery storage chamber  105  to lock the left end and, in that state, the right end is pressed into the battery storage chamber  105 , thereby elastically deforming and then engaging the elastic engaging part  172  with the above described engaged part  110  of the battery storage chamber  105 . With this arrangement, the battery chamber cover  170  is mounted onto the battery storage chamber  105 , as shown in  FIG. 23 . 
     On the other hand, when the battery chamber cover  170  is removed from the battery storage chamber  105 , the operator inserts a finger into the above described engaged part  110  formed into a concave shape and elastically deforms the above described elastic engaging part  172 , thereby disengaging the elastic engaging part  172  and the engaged part  110 . Then, the operator pulls the locking tabs  171  from the locking holes  109  of the battery storage chamber  105 , removing the battery chamber cover  170  from the battery storage chamber  105 . 
     As shown in  FIG. 24  and  FIG. 25 , the elastic engaging part  172  comprises a support part  173  that is arranged in a standing condition from an inner surface  170   a  of the battery chamber cover  170  toward the battery storage chamber  105  side, a curving part  174  provided to the tip of this support part  173 , and the tip part  175  capable of moving toward and away from the above described support part  173  by the flexure of this curving part  174 . A protruding part  175   a  is formed on the tip part  175 , and this protruding part  175   a  engages with the engaged part  110  of the battery storage chamber  105 . 
     Further, a rib part  176  adjacent to the above described support part  173  of the elastic engaging part  172  is arranged in a standing condition on the inner surface  170   a  of the battery chamber cover  170 . This rib part  176  comprises a hollow structure having a cross-section of a substantially sideways u-shape that opens to the left, with the open side connected to the above-described support part  173 . As shown in  FIG. 23 , the rib part  176  functions as a harness pressing part that presses an electric cable  25   a  of a harness  25  connected to the stored rechargeable battery  10  when the battery chamber cover  170  is mounted onto the battery storage chamber  105 . That is, the harness  25  for supplying power to the device is connected to the rechargeable battery  10 , on the right end (left end in  FIG. 23 ) which serves as the other side end thereof, when stored in the battery storage chamber  105 . This harness  25  comprises a connector  25   b  connected to the control substrate  60  previously described, etc., and a plurality (two in this example) of the electric cables  25   a  consolidated into a bundle. These electric cables  25   a  are formed longer in length to allow leeway, taking into consideration detachability during battery replacement. As a result, as shown in  FIG. 23 , when the rechargeable battery  10  is stored in the battery storage chamber  105 , the electric cables  25   a  are looped back within the battery storage chamber  105 . The rib part  176  presses the looped back section of the looped back electric cables  25   a  toward the storage chamber far side, making it possible to prevent interference of the looped back section with the elastic engaging part  172 . 
     In the handheld printer  1  of this embodiment, the metal dome member  39  of the power key  30  is configured to apply a larger reaction force than the metal dome member  49  of the feed key  40 . As a result, to operate the power key  30 , a pressing force that is larger than that when operating the feed key  40  is required. With this arrangement, as shown in  FIG. 7A , even if the operator mistakenly touches the adjacent power key  30  when pressing the feed key  40 , the power key  30  is difficult to press, making it possible to suppress mistaken operation of the power key  30 . As a result, the power of the device is not mistakenly turned off when the feed key  40  is operated, making it possible to normally execute the feed operation. On the other hand, when the operator presses the power key  30 , a relatively large force is required, causing the need to press an accurate position to arise and, as a result, a decrease in the possibility of touching the adjacent feed key  40 , as shown in  FIG. 7B . Accordingly, it is possible to prevent the mistaken operation of the adjacently disposed power key  30  and the feed key  40 . 
     Further, as in this embodiment, since the configuration is one wherein the size of the reaction force applied to each of the keys  30  and  40  is adjusted, it is possible to prevent the mistaken operation of flat-shaped keys as well in comparison to a case where the mistaken operation of adjacent keys is prevented by designing each of the keys  30  and  40  with a convex surface shape, for example. Accordingly, this configuration is advantageous with a handheld electronic device which demands miniaturization and portability. Further, in a case where each of the keys  30  and  40  is made convex in shape as described above, while the contact surface area of the key surface and operator finger significantly decreases, resulting in the concern of a decrease in operability as well as a significant impact on the outer appearance of the device, a resolution can be made according to this embodiment without changing the surface shape of each of the keys  30  and  40 , making it possible to eliminate such above described concern and impact. 
     Further, in particular, according to this embodiment, in a case where the power key  30  and the feed key  40  are simultaneously operated with the power of the handheld printer  1  in an on state, the power key  30  is regarded as having been pressed and the CPU  12  performs power-off processing. That is, in a case where the power key  30  and the feed key  40  are simultaneously pressed with the operation of the power key  30  requiring a larger pressing force than the feed key  40  as in this embodiment, a larger pressing force was most likely applied to the power key  30 . Accordingly, in this case, it can be inferred that the operator pressed the keys with the intention of operating the power key  30 . As a result, the power key  30  is processed with priority as described above, making it possible to perform processing conforming to the intention of the operator. 
     Further, in particular, according to this embodiment, operation of the power key  30  requires a larger pressing force than the feed key  40 . In this state, operating the power key  30  with a larger pressing force while pressing the feed key  40  with just a small pressing force requires less operation labor and is easier than the reverse. Thus, according to this embodiment, the switching of the communication standards of the handheld printer  1  and the external device  2  is assigned as the preset function to such an operation and, in a case where the above described operation is performed with the power in an off state, power-on processing as well as the set switching of the communication standards are executed. With this arrangement, it is possible to execute the switching of the communication standard preferred at power-on using a simple operation, thereby improving user friendliness. 
     Further, in particular, according to this embodiment, the metal dome members  39  and  49  are used in response to the pressing force of the power key  30  and the feed key  40 . Then, the configuration is designed so that the bulging volume h 1  of the bulging part  39   a  of the metal dome member  39  is made greater than the bulging volume h 2  of the bulging part  49   a  of the metal dome member  49 , making the metal dome member  39  apply a larger reaction force than the metal dome member  49 . The bulging volume of each of the bulging parts  39   a  and  49   a  can be easily adjusted by adjusting the punching force when performing punch processing on a metal sheet to form each of the metal dome members, making it possible to achieve a configuration where the metal dome member  39  applies a larger reaction force than the metal dome member  49  based on a simple manufacturing process. Furthermore, a metal member such as the metal dome members  39  and  49  are used, therefore the metal dome members  39  and  49  themselves can be used as electrode contacts, making it possible to simplify the key structure and contact comprise separate members. 
     Further, the handheld printer  1  of this embodiment described above offers the following advantages. That is, the harness  25  for supplying power to the device is connected to the rechargeable battery  10 . This harness  25  comprises a plurality of electric cables  25   a  consolidated into a bundle. These electric cables  25   a  are formed longer in length to allow leeway, taking into consideration detachability at the time of battery replacement, and are therefore looped back within the battery storage chamber  105  when the rechargeable battery  10  is stored in the battery storage chamber  105 . For this reason, in a case where the harness  25  is positioned at the right end of the battery storage chamber  105  as in this embodiment, the possibility exists that the looped back section of the electric cables  25   a  will interfere with the elastic engaging part  172  of the battery chamber cover  170 , impeding elastic deformation thereof and preventing smooth mounting of the battery chamber cover  170  onto the battery storage chamber  105 . 
     Here, according to this embodiment, the rib part  176  configured to press the electric cables  25   a  of the harness  25  is provided near the elastic engaging part  172 . With this arrangement, when the battery chamber cover  170  is mounted onto the battery storage chamber  105 , the looped back section of the electric cables  25   a  of the harness  25  is pressed toward the storage chamber far side by the rib part  176 , making it possible to prevent the looped back section from interfering with the elastic engaging part  172 . As a result, the battery chamber cover  170  can be smoothly mounted onto the battery storage chamber  105 . 
     Further, in particular, according to this embodiment, the elastic engaging part  172  comprises the support part  173  arranged in a standing condition from the inner surface  170   a  of the battery chamber cover  170  toward the inside of the battery storage chamber  105 , the curving part  174  provided to the tip of the support part  173 , and the tip part  175  that engages with the engaged part  110  while moving toward and away from the support part  173  by the flexure of the curving part  174 , and is designed with a configuration that elastically deforms by the flexing movement of the above described curving part  174 . Then, the rib part  176  is adjacently provided to the support part  173 , causing the support part  173  of the elastic engaging part  172  to be securely fixed to the inner surface  170   a  of the battery chamber cover  170 . In this manner, the structure of the elastic engaging part  172  is designed so that the curving part  174  and the tip part  175  elastically deform with respect to the fixed support part  173 , making it possible to decrease the impact on elastic movement when the looped back section of the harness electric cables  25   a  contacts the rib part  176  and the support part  173  in comparison to a structure in which the entire elastic engaging part  172  elastically deforms, thereby making it possible to suppress the interference of the loop backed section with the elastic engaging part  172 . Further, the support part  173  of the elastic engaging part  172  can be securely fixed by the rib part  176 , resulting in the advantage of improving the strength of the elastic engaging part  172  as well. 
     Further, in particular, according to this embodiment, the rib part  176  comprises a hollow structure having a substantially sideways u-shaped cross-section that opens to the left, with the open side connected to the support part  173  of the elastic engaging part  172 . With such a hollow structure, the looped back section of the harness electric cables  25   a  can be reliably pressed toward the storage chamber far side, and the weight can be reduced more than that of a solid structure. 
     Further, in the handheld printer  1  of this embodiment described above, the rubber member  53  is provided between the first boss parts  161 L and  161 R of the top cover  101  and the installation parts  51  and  52  of the chassis assembly  50 . With this arrangement, in a case where the handheld printer  1  is subjected to high impact when dropped, etc., it is possible to absorb the impact transmitted from the top cover  101  to the chassis assembly  50  by the rubber member  53 . As a result, the occurrence of a defect in the platen roller  111  and thermal line head  112  as a result of impact can be suppressed, making it possible to achieve a handheld printer with high impact resistance when dropped, etc. 
     Further, in particular, according to this embodiment, the top cover  101  comprises the rib members  166 L and  166 R around the first boss parts  161 L and  161 R, restricting the movement of the first boss parts  161 L and  161 R toward the installation part  51  and  52  side as the tips of the rib members  166 L and  166 R contact the installation parts  51  and  52  of the chassis assembly  50 . That is, since the rubber member  53  used as an impact absorbing material has the property that its buffering function and durability are decreased when excessively compressed, the provision of the above described rib members  166 L and  166 R makes it possible to prevent the first boss parts  161 L and  161 R from moving toward the installation part  51  and  52  side more than necessary, thereby making it possible to prevent the compression of the rubber member  53  from becoming excessive. Accordingly, it is possible to prevent decreases in the buffering function and durability of the rubber member  53 . 
     Further, in particular, according to this embodiment, the top cover  101  comprises the boss support members  163 L and  163 R configured to support the first boss parts  161 L and  161 R. The boss support members  163 L and  163 R comprise the standing parts  164 L and  164 R arranged in a standing condition on the upper surface of the top cover  101 , and the bending parts  165 L and  165 R provided bending from the standing parts  164 L and  164 R, with the first boss parts  161 L and  161 R provided on the bending parts  165 L and  165 R. With this arrangement, the boss support members  163 L and  163 R are configured to be capable of absorbing the impact transmitted from the top cover  101  to the first boss parts  161 L and  161 R by the flexure that occurs between the standing parts  164 L and  164 R and the bending parts  165 L and  165 R. As a result, the impact transmitted from the top cover  101  to the chassis assembly  50  can be absorbed by not only the rubber member  53  but also the boss support members  163 L and  163 R, thereby further improving the impact durability when the device is dropped, etc. 
     Further, in particular, according to this embodiment, the rubber member  53  is provided between the first boss parts  161 L and  161 R of the top cover  101  and the installation parts  51  and  52 , and not provided between the second boss parts  162 L and  162 R of the undercover  102  and the installation parts  51  and  52 . This is because, with the handheld printer  1 , the top cover  101  covers the major section of the upper and side surfaces of the device contour, and the undercover  102  mainly covers only the lower surface of the device contour, resulting in a configuration in which the top cover  101  covers the major section of the device contour. In this case, there is a high possibility that the top cover  101  that covers the major section of the device contour will be subjected to impact when the handheld printer  1  is dropped, etc. Accordingly, as in this embodiment, the rubber member  53  is provided between the first boss parts  161 L and  161 R of the top cover  101  and the installation parts  51  and  52 , making it possible to effectively absorb an impact transmitted to the chassis assembly  50 . Further, this makes it possible to decrease the number of parts compared to a case where the rubber member  53  is provided between both the first boss parts  161 L and  161 R and the second boss parts  162 L and  162 R and the installation parts  51  and  52 . 
     Further, the handheld printer  1  of this embodiment described above is capable of offering advantages such as the following. That is, in a general handheld printer, the platen roller and thermal line head (including the heat sink, etc.) supported by the side chassis members include metal as a component, and are therefore relatively heavy parts among the parts of the handheld printer. As a result, in a case where the handheld printer is subjected to high impact when dropped, etc., the possibility exists that the pair of side chassis members will deform by opening with respect to one another due to the inertia of the above described heavy objects, causing the platen roller and the thermal line head to separate from the side chassis members. 
     In this embodiment, the base ends of the side chassis members  130 L and  130 R are positioned at both end positions of the main chassis member  150  in a longitudinal direction by the protruding parts  157  provided to both ends of the main chassis member  150  in a longitudinal direction, and the left side chassis member  130 L and the right side chassis member  130 R are connected at a middle position between the base ends of the side chassis members  130 L and  130 R and the providing part of the platen roller  111  or the thermal line head  112  by the front rib part  151  of the main chassis member  150 . With this arrangement, the spacing of the base ends of the side chassis members  130 L and  130 R is fixed to the length of the main chassis member  150  in a longitudinal direction, and the spacing of the middle position between the base ends and the providing part of the platen roller  111  or thermal line head  112  positioned thereabove is also fixed to the length of the main chassis member  150  in a longitudinal direction by the front rib part  151 . 
     Since the spacing of the side chassis members  130 L and  130 R can thus be fixed at two vertical locations, i.e., at the base end and the position thereabove, it is possible to suppress deformation where the pair of side chassis members  130 L and  130 R opens with respect to one another due to the inertia of heavy objects, such as the platen roller  111  and thermal line head  112 , etc., even in a case where the handheld printer  1  is subjected to high impact when dropped, etc., as previously described. As a result, separation of the platen roller  111  and the thermal line head  112  from the side chassis members  130 L and  130 R can be suppressed, making it possible to achieve a handheld printer with high impact resistance when dropped, etc. Further, the configuration is designed so that the main chassis member  150  integrally comprises the protruding parts  157  and the front rib part  151 , making it possible to decrease the number of parts without requiring separate provision of members for positioning and connecting the side chassis members  130 L and  130 R. 
     Further, in particular, according to this embodiment, the configuration is designed so that the left side chassis member  130 L and the right side chassis member  130 R are connected by the front rib part  151  of a cross-sectional L-shape that was formed by bending the front end of the main chassis member  150  along the longitudinal direction toward the disposed side of the platen roller  111  and the thermal line head  112 . That is, since the side chassis members  130 L and  130 R can be connected by simply bending the main chassis member  150 , manufacturing is easy and the structure of the handheld printer  1  can be simplified. Furthermore, the front rib part  151  is formed on the main chassis member  150 , making it possible to increase the strength of the main chassis member  150  itself and design a structure that is even more resistant to the impact that occurs when the handheld printer  1  is dropped, etc. 
     Further, in particular, according to this embodiment, both ends of the front rib part  151  in a longitudinal direction are respectively bent along the planar direction of the side chassis members  130 L and  130 R, forming the first left fixing part  153  and the first right fixing part  154 . With this arrangement, the first left fixing part  153  and the first right fixing part  154  can be made substantially parallel with the planar direction of the side chassis members  130 L and  130 R, making it possible to securely and stably fix both fixing parts  153  and  154  to the side chassis members  130 L and  130 R with the screws  118 . 
     Further, in particular, according to this embodiment, the protruding parts  157  provided to both ends of the main chassis member  150  in a longitudinal direction engage with the engaging holes  134  provided to the base ends of the side chassis members  130 L and  130 R, positioning the base ends of the side chassis members  130 L and  130 R at both end positions of the main chassis member  150  in a longitudinal direction. With such a structure, it is possible to readily position the base ends of the side chassis members  130 L and  130 R at both end positions of the main chassis member  150  in a longitudinal direction based on a simple structure. 
     Further, in the handheld printer  1  of this embodiment described above, the guide member  120  is configured as a separate entity separate from the top cover  101 , the undercover  102 , and the cover member  103  that constitute the housing  100 , and is provided to the side chassis members  130 L and  130 R along with the platen roller  111  and thermal line head  112 . With the platen roller  111 , the thermal line head  112 , and the guide member  120  respectively thus provided to the side chassis members  130 L and  130 R, integral configuration thereof as the chassis assembly  50  is possible. With this arrangement, the relative positional accuracy of the guide member  120  with respect to the platen roller  111  and the thermal line head  112  in relation to the demarcation of the feeding path R of the print-receiving paper S can be improved, regardless of the assembly accuracy of the top cover  101 , the undercover  102 , the cover member  103 , and the chassis assembly  50  during assembly of the handheld printer  1 . This makes it possible to prevent the occurrence of defects caused by the print-receiving paper S contacting an obstacle in the feeding path R, such as the impeding of insertion from the insertion port  104  or paper jams. 
     Further, in particular, according to this embodiment, the beam member  140  forms a bridge across the pair of side chassis members  130 L and  130 R, and the guide member  120  is fixed to the beam member  140  and thus provided to the side chassis members  130 L and  130 R. With such a configuration, the guide member  120  can be reliably fixed to the side chassis members  130 L and  130 R, making it possible to reliably improve the relative positional accuracy of the guide member  120  with respect to the platen roller  111  and the thermal line head  112 . Further, compared to a structure in which the guide member  120  is directly provided to the side chassis members  130 L and  130 R by screws, etc., the guide member  120  can be readily assembled. 
     Further, in particular, according to this embodiment, the guide member  120  comprises the fixing tab members  126  in a plurality of locations in the longitudinal direction, which respectively engage with engaging holes  141  provided to corresponding positions on the front side of the beam member  140 , fixing the guide member  120  to the beam member  140 . With such a structure where a plurality of the fixing tab members  126  engages with the engaging holes  141 , it is possible to securely fix the guide member  120  to the beam member  140 . 
     Further, in particular, according to this embodiment, the beam member  140  comprises among the plurality of engaging holes  141  one positioning hole  143  having a smaller vertical dimension than the other engaging holes  141 . With this arrangement, when the fixing tab members  126  of the guide member  120  are engaged with the engaging holes  141  of the beam member  140 , the vertical position of the guide member  120  can be positioned by the positioning hole  143 . 
     Further, in particular, according to this embodiment, the guide member  120  comprises the hook-shaped hook member  127  in one location in the longitudinal direction, which locks into the locking part  142  provided to a corresponding position on the rear side of the beam member  140 , with the fixing tab members  126  engaged with the engaging holes  141  (including the positioning hole  143 ) on the front side of the beam member  140  as previously described, thereby fixing the guide member  120  to the beam member  140 . With this arrangement, the beam member  140  can be inserted by the fixing tab members  126  and the hook member  127  from both front/rear-direction sides thereof, making it possible to reliably fix the guide member  120  to the beam member  140  while positioning the vertical position thereof. 
     Further, in particular, according to this embodiment, the elevated part  116  made of resin for protecting the semiconductor element that drives the heating element is provided to the surface of the thermal line head  112 . Then, the angle of the inclined surface  122  of the guide member  120  is configured so that the feeding path R that connects the pressing part P of the platen roller  111  and the thermal line head  112  is capable of staying clear of the elevated part  116  of the above described thermal line head  112 , and the positioning holes  141  of the beam member  140  vertically position the guide member  120  so that the feeding path R is capable of staying clear of the elevated part  116 . With this arrangement, it possible to prevent the occurrence of defects caused by the print-receiving paper S contacting the elevated part  116  in the feeding path R, such as the impeding of insertion from the insertion port  104  or paper jams. 
     Further, in the handheld printer  1  of this embodiment described above, the coil spring  115  is provided to the main chassis member  150  that is made of metal and provided on the inner surface of the undercover  102 . With the main chassis member  150  made of metal, strength is increased. Further, by providing the front rib part  150  of a cross-sectional L-shape bent along the longitudinal direction near the provided position of the coil spring  115  of the main chassis member  150 , the strength in response to the reaction force of the coil spring  115  is further improved. With this arrangement, even if the reaction force of the coil spring  115  acts on a plurality of locations in a longitudinal direction, the occurrence of deformation, such as the flexure of the main chassis member  150  in the longitudinal direction, etc., can be prevented, making it possible to suppress variance in the pressing load of the thermal line head  112  caused by the deformation. 
     Further, use of a plurality of the coil springs  115  to energize the thermal line head  112  to the platen roller  111  side makes it possible to suppress the variance in the spring performance in comparison to a case where plate springs, which are susceptible to variance in individual spring performance due to a difference in residual stress when the springs are formed, a difference in the level of metal fatigue caused by use, and the like, are used. Accordingly, the variance in the pressing load of the thermal line head  112  caused by variance in spring performance can be suppressed. 
     Further, in particular, according to this embodiment, the control substrate  60  comprising at the peripheral edge the plurality of concave parts  61  for inserting the coil springs  115  is arranged between the main chassis member  150  and the heat sink  114  that supports the thermal line head  112 . With this arrangement, in a printer configuration where the control substrate  60  is positioned between the main chassis member  150  and the heat sink  114 , a plate spring no longer needs to be used to stay clear of the control substrate  60 , making it possible to achieve a structure in which coil springs, which are not susceptible to variance in individual spring performance, are used. Further, with a configuration in which the concave parts  61  are provided to the peripheral edge of the control substrate  60  for insertion of the coil springs  115  at the outer periphery, it is possible to reduce corrosion of the mounting surface area of the electronic devices of the control substrate  60  compared to a case where insertion holes are provided to the control substrate  60  for insertion of the coil springs  115  at the inner periphery. 
     Further, in particular, according to this embodiment, the spring support shaft  155  is provided in a protruding condition to the main chassis member  150 , and inserted through the coil spring  115 , thereby supporting the coil spring  115 . With this arrangement, the coil spring  115  can be stably supported in a standing condition, and positioned in a predetermined energizing position. 
     Further, in particular, according to this embodiment, the upper end of the coil spring  115  contacts the contact surface  117   a  of the concave spring receiving part  117  provided to the heat sink  114 , energizing the heat sink  114  to the platen roller  111  side. At this time, the contact surface  117   a  of the spring receiving part  117  is formed so that it is orthogonal to the axial direction Y thereof when contacting the coil spring  115 , causing the contact surface  117   a  that contacts the upper end of the coil spring  115  to be held orthogonal to the axial direction Y, even in a case where the posture is not orthogonal to the axial direction Y of the coil spring  115  when in contact with the coil spring  115  due to the rotational movement of the planar direction  1  of the heat sink  114  around the shaft member  113 . With this arrangement, the energizing force of the coil spring  115  can stably act on the heat sink  114 . Further, with the structure designed so that the coil spring  115  directly contacts the heat sink  114 , the heat of the thermal line head  112  can also be transferred from the heat sink  114  to the coil spring  115  and the main chassis member  150  made of metal, resulting in the advantage of the capability of heat radiation as well. 
     Further, in particular, according to this embodiment, the spring receiving part  117  of the heat sink  114  is provided to the front end which is further frontward than the position of the pressing part P of the platen roller  111  in the front/rear direction of the heat sink  114 . With the structure thus designed so that energizing is performed by the coil spring  115  on the front end opposite to the rear end which serves as the rotational center of the heat sink  114 , it is possible to decrease the required energizing force compared to a case where energizing is performed at a middle position of the front end and rear end, enabling miniaturization of the coil spring  115 . Further, the coil spring  115  can be disposed on the outer peripheral side of the device, making it possible to decrease the surface area of the concave part  61  provided to the control substrate  60 . 
     Further, in particular, according to this embodiment, the coil spring  115  that energizes the thermal line head  112  to the platen roller  111  side comprises three coil springs disposed at equal intervals, i.e., the one first coil spring  115 C provided correspondingly to the center position of the thermal line head  112  in a longitudinal direction, and the two second coil springs  115 L and  115 R having a smaller spring constant than the first coil spring  115 C and positioned on both sides of the first coil spring  115 C. With this arrangement, in a case where the handheld printer  1  is a printer that feeds and performs printing on the print-receiving paper S using the center position of the device in a longitudinal direction as standard as in this embodiment, the thermal line head  112  is energized by the first coil spring  115 C having the largest spring constant at the center position in a longitudinal direction which serves as that standard, and energized at both sides by the second coil springs  115 L and  115 R having the smaller spring constant, causing the pressing load of the thermal line head  112  to act with good balance and achieve stability in the longitudinal direction, even if the size of the print-receiving paper S is changed. 
     Note that the present disclosure is not limited to the above described embodiment, and various modifications may be made without deviating from the spirit and scope of the disclosure. The following describes such modifications one by one. 
     (1) When the Feed Key is Prioritized when Keys are Simultaneously Operated 
     While the power key  30  is processed with priority in a case where the power key  30  and the feed key  40  are simultaneously operated according to the above described embodiment, the present disclosure is not limited thereto, allowing prioritization of the feed key  40 . 
     The control details related to the operation of the power key  30  and the feed key  40  executed by the CPU  12  in this modification will now be described with reference to  FIG. 26 . 
     Steps S 10 , S 20 , and S 50  are the same as those in  FIG. 8  previously described. That is, steps S 10  and S 20  are repeated during the period in which the operator does not operate either the power key  30  or the feed key  40 . At this time, in a case where the power key  30  is singly operated, the decision is made that the condition of step S 20  is satisfied and the flow proceeds to step S 50  where the above described power-off processing is executed. 
     On the other hand, in a case where the feed key  40  is operated during the period in which steps S 10  and S 20  are repeated, the flow proceeds to step S 30  where the CPU  12  determines whether or not the power key  30  was simultaneously pressed along with the feed key  40 . At this time, in both cases where the power key  30  was either simultaneously pressed or not pressed, the flow proceeds to step S 40  where the CPU  12  executes the above described feed processing. Then, the flow returns to the above described step S 10 . 
     As described above, according to this modification, in a case where the power key  30  and the feed key  40  are simultaneously operated, feed processing is executed without executing power-off processing. With the processing of the feed key  40  executed with priority in this manner, even if the operator mistakenly applies a larger pressing force to the power key  30  when operating the feed key  40 , thereby simultaneously pressing the power key  30  and feed key  40 , feed processing is executed, making it possible to further increase the function of suppressing mistaken operation of the power key  30 . 
     (2) When the Power Key is Operated by Double-Clicking 
     While operation of the power key  30  and the feed key  40  is performed by pressing the key once according to the above described embodiment, the present disclosure is not limited thereto, allowing the power key  30  to be regarded as operated and power-off processing to be performed only when the key is pressed twice in a row within a predetermined period of time. 
     The control details related to the operation of the power key  30  and the feed key  40  executed by the CPU  12  in this modification will now be described with reference to  FIG. 27 . 
     Steps S 10  and S 20  are the same as those in  FIG. 8  previously described, and are repeated during the period in which the operator does not operate either the power key  30  or the feed key  40 . At this time, in a case where the power key  30  is singly operated, the decision is made that the condition of step S 20  is satisfied and the flow proceeds to step S 25 . 
     In step S 25 , the CPU  12  determines whether or not the power key  30  was pressed twice in a row within a predetermined period of time (hereinafter described as “double-clicked”). In a case where the power key  30  has not been double-clicked, the decision is made that the condition is not satisfied and the flow returns to step S 10 . On the other hand, in a case where the power key  30  was double-clicked, the decision is made that the condition is satisfied and the flow proceeds to step S 50  where the CPU  12  executes power-off processing. This flow then terminates here. 
     On the other hand, in a case where the feed key  40  is operated during the period in which steps S 10  and S 20  (or steps S 10  to S 30 ) are repeated, the decision is made that the condition of step S 10  is satisfied and the flow proceeds to step S 30  where the CPU  12  determines whether or not the power key  30  was simultaneously pressed along with the feed key  40 . In a case where the power key  30  has not been simultaneously pressed, the decision is made that the condition is not satisfied and the flow proceeds to step S 40  where the CPU  12  executes the above described feed processing. Then, the flow returns to the above described step S 10 . On the other hand, in a case where the power key  30  was simultaneously pressed, the decision is made that the condition is not satisfied and the flow proceeds to step S 35 . 
     In step S 35 , the CPU  12  determines whether or not the power key  30  was double-clicked. In a case where the power key  30  was double-clicked, the decision is made that the condition is satisfied and the flow proceeds to the above described step S 50  where the CPU  12  executes power-off processing. On the other hand, in a case where the power key  30  has not been double-clicked, the decision is made that the condition is not satisfied and the flow proceeds to step S 40  where the CPU  12  executes the above described feed processing. Then, the flow returns to the above described step S 10 . 
     As described above, according to this modification, the power key  30  is regarded as pressed and power-off processing is performed only when the power key  30  is double-clicked. With this arrangement, even if the operator mistakenly applies a larger pressing force to the power key  30  when operating the feed key  40 , thereby simultaneously pressing the power key  30  and feed key  40 , feed processing corresponding to the feed key  40  is executed without turning the power off if the keys were pressed once, making it possible to further increase the function of suppressing mistaken operation of the power key  30 . Further, since operation of the power key  30  thus requires the key to be pressed twice, the advantage of the capability of preventing mistaken operation of the power key  30  by a contacting object, etc., at a time other than when operating the feed key  40 , such as when carrying the handheld printer  1 , for example, is also achieved. 
     (3) When the Rubber Member  53  is Provided on the Undercover  102  Side as Well 
     While the rubber member  53  is provided between the first boss parts  161 L and  161 R of the top cover  101  and the installation parts  51  and  52  according to the above described embodiment, the rubber member  53  may be provided between the second boss parts  162 L and  162 R of the undercover  102  and the installation parts  51  and  52  as well. With this arrangement, even in a case where either of the top cover  101  or the undercover  102  is subjected to impact when the handheld printer  1  is dropped, etc., the impact transmitted to the chassis assembly  50  can be reliably absorbed, making it possible to achieve a handheld printer that offers even higher resistance to impact when dropped, etc. 
     (4) When a Locked Structure is Provided to Other Areas in Addition to Both Ends of the Battery Chamber Cover 
     That is, in the above, the battery chamber cover  170  is installed based on a locked and engaged structure at both ends of the battery storage chamber  105 . That is, the locking tabs  171  of the battery chamber cover  170  are locked into the locking holes  109  on the above-described left end side of the battery storage chamber  105 , and the elastic engaging part  172  of the battery chamber cover  170  is engaged with the engaged part  110  on the above described right end side. Nevertheless, the present disclosure is not limited thereto, allowing provision of a locked structure in areas in addition to the above described both ends. The following describes the details of such a modification with reference to each figure, including  FIG. 28  to  FIG. 30 . 
     As previously described, the battery chamber cover  170  is detachably provided to the battery storage chamber  105  provided on the rear side of the housing  100 . With the battery chamber cover  170  removed, the above described battery storage chamber  105  opens to the rear surface section of the housing  100  (refer to  FIG. 22 ). An upper locked part  101   a  and a lower locked part  102   a  for locking the locking and protruding parts  181 A,  181 B, and  182  of the battery chamber cover  170  are provided on the upper side and the lower side of the battery storage chamber  105  (refer to  FIG. 19  and  FIG. 22 ). 
     As described above, the battery chamber cover  170  comprises an upper/lower pair of the above described locking tabs  171  and the above described elastic engaging part  172 . According to this modification, the battery chamber cover  170  further comprises a plurality of the locking and protruding parts  181 A,  181 B, and  182 , as shown in  FIG. 28 ,  FIG. 30A , and  FIG. 30B . The locking and protruding parts  181 A,  181 B, and  182  include at least one first protruding part (two first protruding parts  181 A and  181 B in this example), and at least one second protruding part (one second protruding part  182  in this example). The first protruding parts  181 A and  181 B and the second protruding part  182  are disposed in a substantially staggered manner so that the positions thereof along the longitudinal direction of the above described battery chamber cover  170  differ from each other. According to this example, the first protruding part  181 A, the second protruding part  182 , and the first protruding part  181 B are disposed in a staggered manner in that order along the above described longitudinal direction. At this time, as already shown in  FIG. 2 ,  FIG. 19 ,  FIG. 22 , etc., the upper locked part  101   a  and the lower locked part  102   a  continually extend from one edge part to the other edge part of the opening of the battery storage chamber  105  in a longitudinal direction, and are configured as ribs for preventing the rechargeable battery  10  within the battery storage chamber  105  from slipping off under its own weight. Then, the two first protruding parts  181 A and  181 B are locked into the upper locked part  101   a  configured as a rib as described above, and the one second protruding part  182  is locked into the lower locked part  102   a  configured as a rib as described above. 
     Further, the plurality of locking and protruding parts  181 A,  181 B, and  182  is unevenly disposed in an area of the battery chamber cover  170  other than the above described left end and the above described right end along the above described longitudinal direction, specifically in either the area on the left side or the area on the right side, excluding the center part in a longitudinal direction. Note that, according to this example, the plurality of locking and protruding parts  181 A,  181 B, and  182  is unevenly disposed in the area on the right side (left lower side in  FIG. 25 ) corresponding to the disposed position of the elastic engaging part  172  (in other words, the disposed position of the electric cables  25   a  of the harness  25 ). Note that, to avoid complexities in illustration, the locking and protruding parts  181 A,  181 B, and  182  are not shown other than in  FIGS. 28, 30A, and 30B . 
     In the handheld printer  1  of this modification of the above described configuration, similar to that previously described, when the battery chamber cover  170  is installed to the battery storage chamber  105 , the locking tabs  171  of the battery chamber cover  170  are locked into the locking holes  109  of the battery storage chamber  105  on the above described left end side, and the elastic engaging part  172  of the battery chamber cover  170  is engaged with the engaged part  110  of the battery storage chamber  105  on the above described right end side. 
     Then, according to this modification, the plurality of locking and protruding parts  181 A,  181 B, and  182  is further provided to positions other than the above described both ends (left end and right end) of the battery chamber cover  170  as previously described in order to strengthen the fixed structure in the middle between the above described left end and the above described right end. The first protruding parts  181 A and  181 B are locked into the upper locked part  101 A, and the second protruding part  182  is locked into the lower locked part  102   a . Thus, a locked structure of the battery chamber cover  170  and the battery storage chamber  105  is achieved with an upper side and a lower side in the width direction of the battery chamber cover  170  using sections other than the left end and right end previously described, making it possible to prevent a flexure and rise toward the outer surface side of the battery chamber cover  170 , which can occur in the above described middle. 
     Further, the above described first protruding parts  181 A and  181 B and the second protruding part  182  are arranged in a substantially staggered manner so that the positions thereof along the longitudinal direction of the battery chamber cover  170  are not the same, but different from each other. With this arrangement, when the user removes the battery chamber cover  170  from a mounted state on the battery storage chamber  105 , the resistance that occurs from the above described locked structure that uses each of the protruding parts  181 A,  181 B, and  182  is dispersed, making it possible for the user to relatively easily remove the battery chamber cover  170 . 
     Further, as previously described, when the user mounts the battery chamber cover  170  onto the battery storage chamber  105 , the user first fits the locking tabs  171  into the locking holes  109  on the left end. Subsequently, the user presses and elastically deforms the elastic engaging part  172  on the right end with a finger while maintaining the fit state, thereby engaging the elastic engaging part  172  with the engaged part  110 . Thus, when mounting is performed based on a fixed structure of the left and right ends, when the user hurriedly performs mounting, or in a case where the pressing force is inadequate, etc., the possibility exists that the above described rise will not be completely resolved, causing a portion of the plurality of locking and protruding parts  181 A,  181 B, and  182  positioned in the middle of the left and right ends to not be locked or to be half locked (in an incompletely locked state). 
     Here, in particular, according to this modification, the plurality of locking and protruding parts  181 A,  181 B, and  182  is disposed in a left side area or right side area where the rise height is relatively low, staying clear of the center part in the above described longitudinal direction where the rise height becomes highest as a result of a bend such as previously described. With this arrangement, even in a case where the above described incompletely locked state temporarily occurs, it is possible to suppress the rise height of the locking and protruding parts  181 A,  181 B, and  182  in the unlocked state (or half-locked state) to a low degree. This makes it possible for the user to easily correct the state to the proper completely locked state by pressing the locking and protruding parts  181 A,  181 B, and  182  that are in the unlocked state (or half-locked state) once again. 
     Further, as previously described, when the battery chamber cover  170  is mounted, the locking tabs  171  are first fit into the locking holes  109 , and then the elastic engaging part  172  is engaged with the engaged part  110  by the pressing force of the finger of the user. In particular, according to this modification, the plurality of locking and protruding parts  181 A,  181 B, and  182  is thus disposed on the same side as the elastic engaging part  172  which is lastly pressed by the finger during mounting. With this arrangement, when the elastic engaging part  172  is pressed, the pressing force is caused to simultaneously act on the locking and protruding parts  181 A,  181 B, and  182 , making it possible to smoothly mount the battery chamber cover  170 . 
     Conversely, when the battery chamber cover  170  is removed from the battery storage chamber  105 , the user first elastically deforms the elastic engaging part  172  to disengage the above described engagement as previously described, and then separates the locking tabs  171  from the locking holes  109 . With the plurality of locking and protruding parts  181 A,  181 B, and  182  disposed on the same side as the elastic engaging part  172  first operated by the finger at the time of removal, tensile force acts on the locking and protruding parts  181 A,  181 B, and  182  at the same time as the elastic engaging part  172  is elastically deformed, making it possible to smoothly remove the battery chamber cover  170 . 
     Further, in particular, according to this modification, the plurality of locking and protruding parts  181 A,  181 B, and  182  is disposed on the same side as the electric cables  25   a  of the harness  25  that act on a reaction force, such as the battery chamber cover  170  being pressed toward the outer surface side, thereby reliably suppressing the above described reaction force, making it possible to prevent the rise and flexure of the battery chamber cover  170  toward the outer surface side. 
     Further, in particular, according to this modification, the first protruding part  181 A, the second protruding part  182 , and the first protruding part  181 B are disposed in a staggered manner in that order along the above described longitudinal direction, making it possible to achieve a well-balanced distribution of each of the locking and protruding parts  181 A,  181 B, and  182  and prevent the rise of the battery chamber cover  170 . Further, suppression of the total number of locking and protruding parts  181 A,  181 B, and  182  to three reliably suppresses the resistance that occurs by the locked structure when the user removes the battery chamber cover  170 , making it possible for the user to reliably remove the battery chamber cover  170  with ease. 
     Further, in particular, according to this modification, the upper locked part  101   a  and the lower locked part  102   a  are each configured by a rib that is continually extended from the left side edge part to the right side edge part of the opening of the battery storage chamber  105 . With this arrangement, the ribs provided to prevent the rechargeable battery  10  within the battery storage chamber  105  from slipping off under its own weight are utilized to lock the first protruding parts  181 A and  181 B and the second protruding part  182  and prevent a rise in the battery chamber cover  170 . 
     (5) Other 
     In the above, the arrow shown in the  FIG. 3  denotes an example of signal flow, but the signal flow direction is not limited thereto. Also the present disclosure is not limited to the procedures shown in the above described flowcharts of  FIG. 8 ,  FIG. 26 , and  FIG. 27 , and procedure additions and deletions as well as sequence changes may be made without departing from the spirit and scope of the disclosure. 
     Further, other than that already stated above, techniques based on the above-described embodiments and each of the modifications may be suitably utilized in combination well.