Patent Publication Number: US-9840097-B2

Title: Printer

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims priority from Japanese Patent Application No. 2015-185807, which was filed on Sep. 18, 2015, the disclosure of which is incorporated herein by reference in its entirety. 
     BACKGROUND 
     Field 
     The present disclosure relates to a printer performing printing on a print-receiving medium. 
     Description of the Related Art 
     A printer is already known that can be supplied with power from both an external power source device through an AC adapter and a battery. 
     However, in the prior art, when an AC adapter is mounted, the power supply from a battery is automatically switched to the power supply from an external power source device through the AC adapter. When the AC adapter is removed, the power supply from the external power source device through the AC adapter is automatically switched to the power supply from the battery. Since the power supply from the battery and the power supply from the external power source device through the AC adapter are not independently controlled, this is not necessarily sufficient from the viewpoint of convenience for an operator. 
     SUMMARY 
     It is therefore an object of the present disclosure to provide a printer enabling independent control of the power supply from a battery and the power supply from an external power source device so that the convenience for an operator can be improved. 
     In order to achieve the above described object, according to an aspect of the present application, there is provided a printer comprising a plurality of motion mechanisms including a feeder configured to feed a print-receiving medium and a printing head configured to form a desired print on the print-receiving medium fed by the feeder, a load circuit included in at least one of the plurality of motion mechanisms, a controller that is configured to control voltage supply to the load circuit, and is connected to an input part configured to be supplied with a power source voltage, a power receiving terminal configured to be connected to a power feeding terminal of an external power source device configured to supply a voltage, a first switching circuit that includes a first switch element configured to switch between conduction and interruption in accordance with a first control signal input from the controller, and is connected between the power receiving terminal and the input part, a battery storage part configured to store at least a battery is stored, and a second switching circuit that includes a second switch element configured to switch between conduction and interruption in accordance with a second control signal input from the controller, and is connected between the battery storage part and the input part. 
     The printer of the present disclosure enables both the power supply from the external power source device and the power supply from the battery stored in the battery storage part to the load circuit included in the motion mechanisms such as a feeder and a printing head. 
     These two power supply paths are respectively provided with the first switching circuit and the second switching circuit. In particular, the first switching circuit is disposed between the power receiving terminal connected to the power feeding terminal of the external power source device and the input part of the control circuit controlling the voltage supply to the load circuit. Similarly, the second switching circuit is disposed between the battery storage part in which the battery is stored and the input part of the control circuit. 
     The first switching circuit includes the first switch element, and the first switch element can switch between conduction and interruption in accordance with the first control signal input from a controller. Similarly, the second switching circuit includes the second switch element, and the second switch element can switch between conduction and interruption in accordance with the second control signal input from the controller. 
     As a result, the power supply from the battery and the power supply from the external power source device can independently be controlled. For example, while the external power source device is connected and the battery is housed in the battery storage part, priority is given to the power feeding from the external power source device and, if an instruction is subsequently given for performing high-speed printing (or if the power feeding terminal of the external power source device is pulled out), switching can be performed to give priority to the power feeding from the battery in the battery storage part. As a result, the convenience for an operator can be improved. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view showing an appearance configuration of a portable printer of an embodiment of the present disclosure. 
         FIG. 2  is a side cross-sectional view showing an internal structure of the portable printer taken along a cross section II-II of  FIG. 1 . 
         FIG. 3  is a circuit diagram showing an electric configuration of an AC adapter and the portable printer. 
         FIG. 4  is a table showing forms of first to third control signals during execution of two printing modes. 
         FIG. 5  is a flowchart showing control procedures executed by a CPU. 
         FIG. 6  is a flowchart showing detailed procedures of step S 30 . 
         FIG. 7  is a flowchart showing control procedures executed by the CPU in a modification example of returning to a normal printing mode in accordance with a battery consumption degree. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An embodiment of the present disclosure will now be described with reference to the drawings. This embodiment is an embodiment when the present disclosure is applied to a portable printer serving as a printer. 
     An appearance configuration and an internal structure of a portable printer  1  of this embodiment will be described with reference to  FIGS. 1 and 2 . In the following description, directions toward the lower left side, the upper left side, the upper left side, and the upper right side of  FIG. 1  are forward, backward, leftward, and rightward, respectively. In the following description, the front, rear, left, right, upper, and lower directions stated with respect to each component correspond to the respective directions in the state of the component attached to the portable printer  1 . 
     Overall Configuration 
     In  FIGS. 1 and 2 , the portable printer  1  prints print data received from, for example, an external device (not shown) such as a PC terminal and a portable telephone through wire communication or wireless communication onto various print-receiving mediums S. This portable printer  1  is generally constructed by assembling a substantially rectangular parallelepiped housing  10  forming a device outer contour made of a resin material and a chassis assembly (not shown). 
     The housing  10  includes a top cover  11  forming an upper portion of the device outer contour, a bottom cover  15  forming a lower portion of the device outer contour, and an openable cover member  13  disposed on the front side of an upper surface of the top cover  11 . 
     The housing  10  has a platen roller  111  and a thermal line head  112  disposed therein. The thermal line head  112  is disposed on a radiator plate  114  including a shaft member  113  at an end part on the rear side, and the radiator plate  114  is rotatably supported around the shaft member  113  by side chassis members (not shown). A main chassis member  150  disposed on an inner surface of the bottom cover  15  is provided with a plurality of coil springs  115  rotationally urging the radiator plate  114  supporting the thermal line head  112  toward the platen roller  111 . As a result, the thermal line head  112  can be pressed against the platen roller  111 . 
     A battery storage part  105  storing battery units BT including batteries (not shown) is disposed on the rear side of the housing  10 , and a battery chamber cover  170  is detachably disposed on the battery storage part  105 . While the battery chamber cover  170  is removed, the battery storage part  105  opens in a rear surface portion of housing  100 . 
     The chassis assembly (not shown) includes the main chassis member  150  disposed on the inner surface of the bottom cover  15  and making up a bottom part of the chassis assembly (not shown), and a pair of the side chassis members (not shown) vertically extending from both side end parts in the longitudinal direction of the main chassis member  150 . The side chassis members have shaft holes (not shown) allowing the insertion of a shaft member (not shown) of the platen roller  111  so as to rotatably support the platen roller  111 . The platen roller  111  is rotationally driven by a drive motor  53  (see  FIG. 3  described later) to feed a print-receiving medium S. The side chassis members rotatably support the radiator plate  114  including the thermal line head  112  via the shaft member  113  described above. 
     The chassis member on the left side is provided with the drive motor  53  driving the platen roller  111  and a gear mechanism (not shown) made up of a plurality of gears transmitting a drive force of the drive motor  53  to the shaft member of the platen roller  111 . 
     A beam member (not shown) is stretched between upper portions of the side chassis members and fixed by screws. A guide member  12  guiding the print-receiving medium S inserted into the insertion port  14  to a pressing part P between the platen roller  111  and the thermal line head  112  is formed as a separate member separated from the top cover  11 , the bottom cover  15 , and the cover member  13  making up the housing  10  and is disposed on the side chassis members by being fixed to the beam member. The insertion port  14  is formed into a substantially slit-like shape by a gab leading to the pressing part P between the guide member  12  and the cover member  13  and has a size capable of accommodating the maximum width size of the print-receiving medium S. 
     The guide member  12  has an upper part provided with a horizontal surface substantially horizontal when being assembled to the chassis assembly (not shown) and a slope inclined from the horizontal surface toward the inside of the device. On the horizontal surface and the slope, a plurality of rib parts formed along the guiding direction of the print-receiving medium S is arranged in parallel in the longitudinal direction. 
     &lt;General Operation&gt; 
     In the configuration, at the time of printing, the print-receiving medium S is inserted into the insertion port  14  formed between the top cover  11  and the cover member  13  with the cover member  13  closed. The inserted print-receiving medium S is guided by the guide member  12  disposed under the insertion port  14  to the pressing part P between the platen roller  111  and the thermal line head  112 . The platen roller  111  comes into contact with the print-receiving medium S at a predetermined pressing force to feed the print-receiving medium S. The thermal line head  112  performs desired printing onto the fed print-receiving medium S. After completion of the printing, the print-receiving medium S is discharged from a discharge port  17  formed between the cover member  13  and the bottom cover  15 . A sheet detection sensor Se is disposed on a feeding path to the discharge port  17  of the print-receiving medium S (e.g., near the insertion port  14 ). Based on a detection result of the sheet detection sensor Se, the feed by the platen roller  111  and the printing by the thermal line head  112  are controlled. In the case of jamming of paper etc., the cover member  13  is opened to release the platen roller  111  from the thermal line head  112  so that the print-receiving medium S can easily be pulled out. 
     On the left side of the top cover  11 , the upper part of the housing  10  includes a feed key  20  for performing a sheet feeding operation, a power key  30  for performing a power on/off operation, and a mode switching button  40  for switching a mode of printing speed described later in this order from the rear side (the mode may be switched from a personal computer etc. connected separately). 
     &lt;Circuit Configuration&gt; 
     A circuit configuration of the portable printer  1  characterizing this embodiment will be described with reference to  FIG. 3 . As shown in  FIG. 3 , the portable printer  1  of this embodiment can be supplied with power from both the an AC adapter  34  making up a portion of an external power source device (it is noted that the AC adapter  34  is removed from the portable printer  1  in the state shown in  FIG. 3 ) and the batteries BT stored in the battery storage part  105 . 
     &lt;Circuit Overview&gt; 
     In particular, the portable printer  1  is provided with the battery storage part  105  storing a plurality of (in this example, six) batteries BT, a first switching circuit G 1 , a second switching circuit G 2 , a third switching circuit G 3 , a constant voltage circuit (linear regulator)  51  capable of outputting a constant voltage (in this example, 3.3 VB), a CPU  52  made up of a microcomputer etc., and performing predetermined calculations, a drive motor  53  including a coil, a drive circuit  54  connected to the drive motor  53 , the thermal line head  112  including a plurality of heat generation elements (not shown), LEDs  9  made up of a plurality of light-emitting diodes connected to the CPU  52 , and an EEPROM  55  connected to the CPU  52  and capable of storing data. 
     &lt;Battery Storage Part&gt; 
     In the battery storage part  105 , the batteries BT are stored in series. A series of these six batteries BT is grounded on the cathode side. The anode side of the series of these six batteries BT is connected to the second switching circuit G 2  including a second switching element  102 . 
     &lt;AC Adapter&gt; 
     On the other hand, the AC adapter  34  for the power supply from the external power source device has an AC plug  34 C connected to an AC outlet (not shown) side of the external power source device capable of supplying a voltage, a voltage conversion part  34 D connected to the AC plug  34 C, and a DC plug  34 E connected to the voltage conversion part  34 D and supplied with a predetermined voltage (in this example, 15 V). A DC plug  34 E has a first terminal  34 A on the negative side and a second terminal  34 B on the positive side. 
     &lt;DC Jack&gt; 
     Accordingly, the portable printer  1  includes a DC jack  33  to which the DC plug  34 E can be connected. The DC jack  33  includes a first terminal  33 A on the negative side that is to be connected with the first terminal  34 A of the DC plug  34 E and that is connected to a negative-side bus line, and a second terminal  33 B on the positive side that is to be connected with the second terminal  34 B of the DC plug  34 E and that is connected to a positive-side bus line. The first terminal  33 A is grounded via a back flow preventing diode  33 C, and the second terminal  33 B is connected to the first switching circuit G 1 . 
     &lt;First Switching Circuit&gt; 
     The first switching circuit G 1  is made up of a P-channel MOSFET  101  switching between conduction and interruption in accordance with a first control signal  51  input from the CPU  52 , an NPN transistor Tr 1 , and resistors R 1 , R 2 , R 3 , R 4 . 
     The source side of the first switch element  101  is connected to the second terminal  33 B of the DC jack  33 . 
     The drain side of the first switch element  101  is connected via the back flow preventing diode  50 A to a power source line VH having the constant voltage circuit  51 , the drive motor  53 , and the thermal line head  112  serving as loads. 
     The source side of the first switch element  101  is also connected via the resistor R 1  to the gate side of the first switch element  101 . The gate side of the first switch element  101  is connected via the resistor R 2  to the collector side of the transistor Tr 1 . The emitter side of the transistor Tr 1  is grounded, and the resistor R 4  is disposed to connect the base side and the emitter side (ground side) of the transistor Tr 1 . The base side of the transistor Tr 1  is connected via the resistor R 3  to a first general-purpose output port of the CPU  52  to form a path of the first control signal S 1 . 
     The source side of the first switch element  101  is connected via a voltage-dividing circuit  104 A to an AD conversion input port of the CPU  52 , and a detection voltage VA (adapter voltage) is input to the CPU  52 . 
     &lt;Second Switching Circuit G 2 &gt; 
     The second switching circuit G 2  has a configuration equivalent to the first switching circuit G 1  and is made up of a P-channel MOSFET  102  switching between conduction and interruption in accordance with a second control signal S 2  input from the CPU  52 , an NPN transistor Tr 1 , and resistors R 1 , R 2 , R 3 , R 4 . 
     The source side of the second switch element  102  is connected to the anode side of the batteries BT. The drain side of the second switch element  102  is connected to a boosting circuit  103 . 
     As is the case with the first switch element  101 , the source side of the second switch element  102  is also connected via the resistor R 1  to the gate side of the second switch element  102  and is further connected via the resistor R 2  to the collector side of the transistor Tr. The emitter side of the transistor Tr 1  is grounded, and the resistor R 4  is disposed to connect the base side and the emitter side (ground side). The base side of the transistor Tr 1  is connected via the resistor R 3  to the second general-purpose output port of the CPU  52  to form a path of the second control signal S 2 . 
     The source side of the second switch element  102  is connected via a voltage-dividing circuit  104 B to the AD conversion input port of the CPU  52 , and a detection voltage VB (battery voltage) is input to the CPU  52 . 
     &lt;Boosting Circuit&gt; 
     The boosting circuit  103  boosts a terminal voltage from the batteries BT stored in the battery storage part  105  to a predetermined voltage (in this example, 15 V). The load side of the boosting circuit  103  is connected via a back flow preventing diode  50 B to the power source line VH. As a result, the load side of the first switching circuit G 1  and the load side of the boosting circuit  103  electrically form OR connection via the back flow preventing diodes  50 A,  50 B and are connected to the power source line VH. 
     &lt;Operations of First Switching Circuit G 1 , Second Switching Circuit G 2 , Boosting Circuit&gt; 
     The operations of the first switching circuit G 1  and the second switching circuit G 2  having the above configuration will be described. In this embodiment, a threshold value related to the gate voltage of the first switch element  101  and the second switch element  102  is set to, for example, 1.0 [V] (or −1.0 [V]) and, if a gate voltage VGS (a gate voltage from the viewpoint of the source side of the first and second switch elements  101 ,  102 ) exceeds this voltage, the first switch element  101  and the second switch element  102  are made conductive. In this embodiment, the P-channel first and second switch elements  101 ,  102  are switched by a high-level signal H or a low-level signal L from the first and second general-purpose output ports of the CPU  52  so as to switch conduction and interruption of the first switching circuit G 1  and the second switching circuit G 2 . 
     In particular, when the first control signal S 1  from a first general-purpose output port of the CPU  52  is the high-level signal H, the transistor Tr 1  is put into the ON state in the first switching circuit G 1 . As a result, the gate voltage VGS of the first switch element  101  has a value (e.g., −1.6 [V]) exceeding the threshold value of −1.0 [V] and the first switch element  101  is made conductive. On the other hand, when the first control signal S 1  from the first general-purpose output port of the CPU  52  is the low-level signal L, the transistor Tr 1  is put into the OFF state in the first switching circuit G 1 , and the gate voltage VGS of the first switch element  101  is set to 0[V], which makes the first switch element  101  non-conductive. 
     Similarly in the second switching circuit G 2 , when the second control signal S 2  from a second general-purpose output port of the CPU  52  is the high-level signal H, the transistor Tr 1  is put into the ON state. As a result, the gate voltage VGS of the second switch element  102  has a value (e.g., −1.6[V]) exceeding the threshold value of −1.0 [V] and the second switch element  102  is made conductive. On the other hand, when the first control signal S 2  form the second general-purpose output port of the CPU  52  is the low-level signal L, the transistor Tr 1  is put into the OFF state in the second switching circuit G 2 , and the gate voltage VGS of the second switch element  102  is set to 0[V], which makes the second switch element  102  non-conductive. 
     Additionally, the boosting circuit  103  includes a boost switching terminal (enable input) for switching between direct conduction and boosted conduction. When the third control signal S 3  from a third general-purpose output port of the CPU  52  is the high-level signal H, the boosting circuit  103  is switched to a boosted conduction state so that the terminal voltage from the batteries BT is boosted to 15 V described above and supplied toward the back flow preventing diode  50 B. When the third control signal S 3  from the third general-purpose output port of the CPU  52  is the low-level signal L, the boosting circuit  103  is switched to a direct conduction state so that the terminal voltage from the batteries BT is supplied directly (without boosting) toward the back flow preventing diode  50 B. 
     &lt;Third Switching Circuit G 3 &gt; 
     The third switching circuit G 3  is a circuit switching ON/OFF of a Vcc power source and includes transistors Tr 4 , Tr 5  and resistors R 11 -R 14 . The base side of the transistor Tr 4  is connected via the resistor R 14  to the CPU  52 , and the resistor R 13  is disposed to connect the base side and the emitter side (ground side) of the transistor Tr 4 . The collector side of the transistor Tr 4  is connected via the resistor R 12  to the base side of the transistor Tr 5 , and the emitter side of the transistor Tr 5  is connected to a Vdd terminal of the CPU  52 . The emitter side and the base side of the transistor Tr 5  are connected via the resistor R 11 , and the collector side of the transistor Tr 5  acts as an output end of a predetermined voltage (3.3 Vcc) and is connected to the LEDs  9  and the EEPROM  55 . 
     In the third switching circuit G 3  having the above configuration, an ON/OFF control signal from the CPU  52  switches the transistor Tr 2  and the transistor Tr 1  to ON or OFF, thereby controlling the power feeding to the LEDs  9  and the EEPROM  55 . 
     &lt;Switching of Two Modes&gt; 
     As described above, in the portable printer  1  of this embodiment, the first switching circuit G 1  includes the first switch element  101 , and the first switch element  101  can switch between conduction and interruption in accordance with the first control signal S 1  input from the outside. Similarly, the second switching circuit G 2  includes the second switch element  102 , and the second switch element  102  can switch between conduction and interruption in accordance with the second control signal S 2  input from the outside. The AC adapter  34  includes a current limiting circuit in consideration of the safety at the time of a short circuit. On the other hand, rechargeable batteries with a large allowable output current are used for the batteries BT. Therefore, the portable printer  1  can perform printing while switching two modes, i.e., a normal printing mode of printing at a (predefined) normal printing speed with larger power from the external power source device through the AC adapter  34  and a high-speed mode of printing at a printing speed higher than the normal printing speed with power from the batteries BT. This mode switching is executed by the CPU  52  outputting the first to third control signal S 1 -S 3  in accordance with an operation of the mode switching button  40  described above and an input of a corresponding operation signal to the CPU  52  (or in accordance with an operation signal input to the CPU  52  due to an operation etc. from an external personal computer (PC)), for example. 
     &lt;Normal Printing Mode&gt; 
     In particular, as shown in  FIG. 4 , during execution of the normal printing mode, the first control signal S 1  output by the CPU  52  is set to the high-level signal H to make the first switch element  101  of the first switching circuit G 1  conductive, while the second control signal S 2  is set to the low-level signal L to interrupt the second switch element  102  of the second switching circuit G 2 , and the third control signal S 3  is set to the low-level signal L to put the boosting circuit  103  into the direct conduction state. As a result, the voltage of 15 V supplied from the external power source device and converted by the voltage conversion part  34 D of the AC adapter  34  is supplied through the DC jack  33 , the first switching circuit G 1 , and the back flow preventing diode  50 A to the constant voltage circuit  51 , the drive motor  53 , the thermal line head  112 , etc., and the printing is performed in the normal printing mode. In this embodiment, if the AC adapter  34  is mounted, the CPU  52  preferentially executes the normal printing mode in principle regardless of whether the batteries BT are stored in the battery storage part  105  (with exceptions such as when the button  40  is operated to give an instruction for switching to a high-speed printing mode). 
     &lt;High-Speed Printing Mode&gt; 
     During execution of the high-speed printing mode, the first control signal S 1  output by the CPU  52  is set to the low-level signal L to interrupt the first switch element  101  of the first switching circuit G 1 , while the second control signal S 2  is set to the high-level signal H to make the second switch element  102  of the second switching circuit G 2  conductive, and the third control signal S 3  is set to the high-level signal H to put the boosting circuit  103  into the boosted conduction state. As a result, the voltage of 7.2 V supplied from the batteries BT of the battery storage part  105  is sent through the second switching circuit G 2  and boosted to 15V by the boosting circuit  103  and is then supplied through the back flow preventing diode  50 B to the constant voltage circuit  51 , the drive motor  53 , the thermal line head  112 , etc., and the printing is performed in the high-speed printing mode. In the embodiment, if the AC adapter  34  is not mounted and the batteries BT are stored in the battery storage part  105 , the CPU  52  always executes the high-speed printing mode. 
     &lt;Automatic Return from High-Speed Printing Mode to Normal Printing Mode&gt; 
     Additionally, in this embodiment, not only are the two printing modes simply selectively switched as described above, but also the printing mode may be returned to the normal printing mode when print formation is completed for a predetermined unit amount of the print-receiving mediums S (in this example, a predetermined number of sheets to be printed. for example, one or several A4 sheets) after switching from the normal printing mode to the high-speed printing mode (triggered by input of the operation signal described above), for example. 
     &lt;Control Procedures&gt; 
     Control procedures executed by the CPU  52  for performing an automatic return function from the high-speed printing mode to the normal printing mode will be described with reference to  FIGS. 5 and 6 . 
     In a flow shown in  FIG. 5 , first, at step S 10 , the CPU  52  initializes a high-speed printing mode switching flag F=0 and goes to step S 20 . 
     At step S 20 , the CPU  52  inputs the print data for printing on the print-receiving mediums S and the number of the print-receiving mediums S to be printed in accordance with, for example, an operation of an appropriate operation part of the portable printer  1  (or an appropriate input operation on an external personal computer). 
     Subsequently, at step S 30 , the CPU  52  executes a mode instruction input process of inputting an execution instruction for selectively executing the normal printing mode or the high-speed printing mode. 
     Detailed procedures of the mode instruction input process of step S 30  will be described with reference to  FIG. 6 . In  FIG. 6 , first, at step S 31 , the CPU  52  determines whether the AC adapter  34  is mounted on (connected to) the DC jack  33  of the portable printer  1 , with a known appropriate technique. If not mounted, the determination of step S 31  is negative (S 31 :NO) and the CPU  52  goes to step S 36  described later. If mounted, the determination of step S 31  is affirmative (S 31 :YES) and the CPU  52  goes to step S 32 . 
     At step S 32 , the CPU  52  determines whether an operator performs a switching instruction operation for the high-speed printing mode through the mode switching button  40 , for example. If the switching instruction operation is not performed, the determination of step S 32  is negative (S 32 :NO) and the CPU  52  goes to step S 37  described later. If the instruction operation for switching is performed, the determination of step S 32  is affirmative (S 32 :YES) and the CPU  52  goes to step S 33 . 
     At step S 33 , the CPU  52  determines whether the batteries BT are mounted on the battery storage part  105 , with a known appropriate technique. If the batteries BT are not mounted, the determination of step S 33  is negative (S 33 :NO) and the CPU  52  goes to step S 37  described later. If the batteries BT are mounted, the determination of step S 33  is affirmative (S 33 :YES) and the CPU  52  goes to step S 34 . 
     At step S 34 , in accordance with the fact that (although the normal printing mode is normally executed without change because the AC adapter  34  is mounted) the instruction for the high-speed printing mode is given due to the intention of the operator (see step S 32  described above), the CPU  52  sets the high-speed printing mode switching flag to F=1 and goes to step S 35 . 
     At step S 35 , the CPU  52  sets a mode instruction to “H” corresponding to the high-speed printing mode. Subsequently, the CPU  52  goes to step S 40  of  FIG. 5  described later. 
     On the other hand, at step S 36  after the negative determination of step S 31 , as is the case with step S 33 , the CPU  52  determines whether the batteries are mounted on the battery storage part  105 , with a known method. If the batteries are not mounted, the determination of step S 36  is negative (S 36 :NO) and the CPU  52  directly goes to step S 40  of  FIG. 5 . If the batteries are mounted, the determination of step S 36  is affirmative (S 36 :YES) and the CPU  52  goes to step S 35  to set the mode instruction to “H.” Subsequently, the CPU  52  goes to step S 40  of  FIG. 5 . 
     On the other hand, at step S 37  after the negative determination of step S 32  or step S 33 , in accordance with the fact that no particular instruction is given by the operator for switching to the high-speed printing mode while the AC adapter  34  is mounted or that, although the instruction is given for the switching, the batteries BT are not stored in the battery storage part  105 , the CPU  52  sets the mode instruction to “L” corresponding to the normal printing mode. Subsequently, the CPU  52  goes to step S 40  of  FIG. 5  described later. 
     Returning to  FIG. 5 , after step S 30  is completed as described above, the CPU  52  goes to step S 40 . At step S 40 , the CPU  52  determines whether the mode instruction is “H” at step S 30 . If the mode instruction is “L,” the determination of step S 40  is negative (S 40 :NO) and the CPU  52  goes to step S 100  described later. If the mode instruction is “H,” the determination of step S 40  is affirmative (S 40 :YES) and the CPU  52  goes to step S 50 . 
     At step S 50 , the CPU  52  determines whether the high-speed printing mode switching flag F is 1. If F=0, the determination of step S 50  is negative (S 50 :NO) and the CPU  52  goes to step S 70  described later. On the other hand, if the F=1 is set because the operator intentionally gives an instruction for the high-speed printing mode while the AC adapter  34  is mounted as described above (see step S 34 ), the determination of step S 50  is affirmative (S 50 :YES) and the CPU  52  goes to step S 60 . 
     At step S 60 , the CPU  52  determines whether the printing of the predetermined number (predetermined unit amount) of the sheets S to be printed is completed. If the printing of the predetermined number of the sheets is completed after the operator intentionally gives the instruction for switching to the high-speed mode as described above, the determination of step S 60  is affirmative (S 60 :YES and the CPU  52  goes to step S 110  described later. If the printing of the predetermined number of the sheets is not completed, the determination of step S 60  is negative (S 60 :NO) and the CPU  52  goes to step S 70 . 
     At step S 70 , the CPU  52  sets the printing mode to the high-speed printing mode. In particular, the CPU  52  outputs the low-level signal L as the first control signal S 1  to the first switching circuit G 1  and outputs the high-level signal H as the second control signal S 2  to the second switching circuit G 2 . As a result, the first switching circuit G 1  is made non-conductive, and the second switching circuit G 2  is made conductive. Additionally, the CPU  52  outputs the high-level signal H as the third control signal S 3  to the boosting circuit  103  and, as a result, the boosting circuit  103  is put into the boosted conduction state. Consequently, the power feeding from the external power source device capable of voltage supply through connection of the AC adapter  34  is interrupted, and the power from the batteries in the battery storage part  105  is boosted and supplied to the constant voltage circuit  51 , the drive motor  53 , the thermal line head  112 , etc. Subsequently, the CPU  52  goes to step S 80  described later. 
     On the other hand, at step S 100  after the negative determination of step S 40 , the CPU  52  determines whether the mode instruction is “L.” If the mode instruction is not “L,” the determination of step S 100  is negative (S 100 :NO) and the CPU  52  goes to step S 120  for error display by the LEDs  9  (e.g., by making the third switching circuit G 3  conductive) and then terminates this flow. 
     If the mode instruction is “L,” the determination of step S 100  is affirmative (S 100 :YES) and the CPU  52  goes to step S 110 . As described above, if the determination of step S 60  is affirmative (if the printing of the predetermined number of sheets is completed after the operator intentionally gives the instruction for switching to the high-speed mode), the CPU  52  also goes to step S 110 . At step S 110 , the CPU  52  sets the printing mode to the normal printing mode. In particular, the CPU  52  outputs the high-level signal H as the first control signal S 1  to the first switching circuit G 1  and outputs the low-level signal L as the second control signal S 2  to the second switching circuit G 2 . As a result, the first switching circuit G 1  is made conductive and the second switching circuit G 2  is made non-conductive. Additionally, the CPU  52  outputs the low-level signal L as the third control signal S 3  to the boosting circuit  103  and, as a result, the boosting circuit  103  is put into the direct conduction state. Consequently, the power feeding from the batteries BT in the battery storage part  105  is interrupted, and the power from the external power source device is supplied through the AC adapter  34  to the constant voltage circuit  51 , the drive motor  53 , the thermal line head  112 , etc. Subsequently, the CPU  52  goes to step S 80 . 
     At step S 80 , the CPU  52  performs a printing process of printing the print data input at step S 20  onto the print-receiving medium S in the printing mode that has been set at this time point (the high-speed printing mode set at step S 70  or the normal printing mode set at step S 110 ). 
     Subsequently, at step S 90 , the CPU  52  determines whether the printing process of step S 80  is completed for all the number of sheets input at step S 20 . If the printing of all the number of sheets is not yet completed, the determination of step S 90  is negative (S 90 :NO) and the CPU  52  returns to step S 30  to repeat the same procedure. If the printing of all the number of sheets is completed, the determination of step S 90  is affirmative (S 90 :YES) and the CPU  52  terminates this flow. 
     By executing the flow described above, if the operator gives an instruction for shifting to the high-speed printing mode in the state of the normal printing mode (i.e., while the AC adapter  34  is mounted), the printing mode can subsequently automatically be returned to the normal printing mode, without performing a particular return instruction operation for the normal printing mode, after a predetermined unit amount of print formation (in this example, a predetermined number of sheets to be printed. alternatively, a predetermined print length or a predetermined print range area may be specified). 
     As described above, in the portable printer  1  of this embodiment, the first switching circuit G 1  includes the first switch element  101  capable of switching between conduction and interruption in accordance with the first control signal S 1 , and the second switching circuit G 2  includes the second switch element  102  capable of switching between conduction and interruption in accordance with the second control signal S 2 . As a result, the power supply from the batteries BT and the power supply from the external power source device (through the AC adapter  34 ) can independently be controlled. In particular, as described above, for example, while the AC adapter  34  is mounted and the batteries BT are stored in the battery storage part  105 , priority is given to the power feeding from the external power source device through the AC adapter  34  and, if an instruction is subsequently given for executing the high-speed printing mode (or if the power feeding terminal of the external power source device is pulled out), switching can be performed to give priority to the power feeding from the batteries BT in the battery storage part  105 . As a result, the convenience for an operator can be improved. 
     Particularly in this embodiment, the boosting circuit  103  for boosting the terminal voltage from the batteries BT is connected between the second switching circuit G 2  and the constant voltage circuit  51 . As a result, even if the batteries BT are consumed and the terminal voltage becomes lower, a voltage of a predetermined level (in the above example, 15V) can reliably be supplied to the load side. 
     In this regard, particularly in this embodiment, as described above, the printing modes can be switched and utilized between the normal printing mode of printing at the normal printing speed with the power supplied from the external power source device and the high-speed printing mode of printing at the high printing speed with the power supplied from the batteries BT. In this case, the CPU  52  outputs the first to third control signals S 1 -S 3  so as to selectively execute the normal printing mode or the high-speed printing mode in accordance with the input operation signal. Consequently, these two printing modes can smoothly be switched. 
     Particularly in this embodiment, as described above with reference to the flows of  FIGS. 5 and 6 , after the operator performs an operation of giving an instruction for shifting to the high-speed printing mode in the state of the normal printing mode, the printing mode can automatically be returned to the the normal printing mode after the predetermined unit amount of print formation, without performing a particular return instruction operation for the normal printing mode. Particularly, since a large current is supplied from the batteries BT to the load side in the high-speed printing mode, the batteries BT can reliably be prevented from being heavily consumed because of accidentally forgetting to perform the return instructing operation. 
     The present disclosure is not limited to the embodiment and may variously be modified without departing from the spirit and the technical ideas thereof. Such modification examples will hereinafter be described in order. 
     (1) When Normal Printing Mode Is Automatically Returned in Accordance with Consumption Degree of Batteries 
     Although the return from the high-speed printing mode to the normal printing mode is triggered by completion of the predetermined unit amount of printing in the embodiment, this is not a limitation, and the return from the high-speed printing mode to the normal printing mode may be triggered by reaching a certain level of consumption of the batteries BT. 
       FIG. 7  is a flowchart showing control procedures executed by the CPU  52  in this modification example. In the flow shown in  FIG. 7 , step S 60 ′ is provided instead of step S 60  of  FIG. 5 . At step S 60 ′, the CPU  62  determines whether a consumption degree of the batteries reaches a predetermined threshold value defined in advance. In particular, as described above, to the AD conversion input port of the CPU  52 , the terminal voltage of the batteries BT is input as the detection voltage VB to the CPU  52  (a function of the CPU  52 ). At step S 60 ′, based on the input detection voltage VB, a consumption degree of the batteries BT is determined in accordance with whether a voltage drop amount of the batteries BT stored in the battery storage part  105  reaches a predetermined value defined in advance. If the voltage drop amount reaches the predetermined value or more, the CPU  52  considers that a consumption degree of the batteries BT reaches the predetermined threshold value and, therefore, the determination of step S 60 ′ is affirmative (S 60 ′:Yes) and the CPU  52  goes to step S 110  to return to the normal printing mode. 
     The flowchart is the same as  FIG. 6  except step S 60 ′ and will not be described. 
     In this variation example, after the operator performs an operation of giving an instruction for shifting to the high-speed printing mode in the state of the normal printing mode, the printing mode is automatically returned to the normal printing mode when the batteries are consumed to some extent, without performing a particular return instruction operation for the normal printing mode. As a result, in the same way as above, the batteries can reliably be prevented from being accidentally heavily consumed. 
     (2) Other Variations of Switching 
     Although the first control signal S 1 , the second control signal S 2 , and the third control signal are all switched between the high-level signal H and the low-level signal L in the above description, this is not a limitation. In particular, if the switching control between the high-level signal H and the low-level signal L is carried out for the third control signal S 3 , the second control signal S 2  may always be set to the high-level signal H (on the basis that the batteries BT are mounted). This is because the configuration shown in  FIG. 3  has a so-called wired OR connection (a connection form in which a plurality of output signals is wired by using diodes) through the back flow preventing diodes  50 A,  50 B and the power is automatically supplied from the higher voltage side between the AC adapter  34  and the batteries BT. 
     Alternatively, the second control signal S 2  may normally be set to the high-level signal H as described above and may be set to the low-level signal L when the output voltage (terminal voltage) of the batteries BT becomes less that a predetermined value (e.g., 4.2 [V]). This produces the effect that the degradation due to over discharge of the batteries BT can be prevented. 
     (3) Others 
     The arrows shown in  FIG. 3  indicate an example of signal flow and are not intended to limit the signal flow directions. 
     The flowcharts shown in  FIGS. 5, 6, and 7 . are not intended to limit the present disclosure to the procedures shown in the flows and the procedures may be added/deleted or may be executed in different order without departing from the spirit and the technical ideas of the disclosure. 
     The techniques of the embodiment and the modification examples may appropriately be utilized in combination other than those described above.