Patent Publication Number: US-2011063649-A1

Title: Printer and task control method

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2009-214648, filed on Sep. 16, 2009, the entire contents of which are incorporated herein by reference. 
     FIELD 
     Embodiments described herein relate to a printer, program and a task control method. 
     BACKGROUND 
     A portable printer is widely used in such applications as door-to-door delivery and inventory management. In one method of using the portable printer, a label with a backing sheet is wound in a roll and loaded into the portable printer. The portable printer pulls the labels through the printer and prints accumulated print data onto the labels which are bonded to the backing sheet. The printed labels are separated from the backing sheet and dispensed from a paper outlet. 
     In the aforementioned portable printer, after a specified time period has lapsed from a standby mode while being operated with the rechargeable battery, the standby mode is changed over to an energy-saving sleep mode to reduce power consumption. 
     When in the sleep mode, however, the processing speed of a central processing unit for controlling each of the units is reduced approximately by one half. Since the processing speed of the central processing unit is slowed in the sleep mode, a problem occurs since the processing of a specified task is delayed. For example, when driving the portable printer, a charge monitoring task for monitoring the charging state of a rechargeable battery precedes a roaming task for searching for a base station through a wireless LAN mounted on the portable printer. In this case, there may be a problem in that the roaming (i.e., searching for a base station) is delayed for a long period, consequently interrupting wireless communication halfway. 
     In other words, the charge monitoring task for monitoring the charging state of a rechargeable battery in the portable printer is of paramount importance when the battery is charging, but is not so important during the printer driving period. Nevertheless, the charge monitoring task has higher priority during the print driving period, which is problematic. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view showing the outward appearance of a portable printer according to one embodiment. 
         FIG. 2  is a perspective view showing the outward appearance of the portable printer whose cover is opened. 
         FIG. 3  is a schematic diagram illustrating a paper path. 
         FIG. 4  is a block diagram showing a control system employed in the portable printer. 
         FIG. 5  is a block diagram showing the configuration of a print controller. 
         FIG. 6  is a function block diagram illustrating a function associated with task control processing. 
         FIG. 7  is a flowchart illustrating a flow of task control processing. 
     
    
    
     DETAILED DESCRIPTION 
     According to one embodiment, there is provided a printer that includes: a direct current power input unit supplied with direct current power; a rechargeable battery capable of being charged with the direct current power inputted from the direct current power input unit; and a task priority changing unit for determining the operational priority of a charge monitoring task to be higher than the operational priorities of other tasks when the rechargeable battery is being charged with the direct current power inputted from the direct current power input unit, and for determining the operational priority of the charge monitoring task to be lower than the operational priority of at least one of the other tasks when the rechargeable battery is not being charged with the direct current power inputted from the direct current power input unit. 
     According to another embodiment, there is provided a program for causing a computer used in controlling a printer including a direct current power input unit supplied with direct current power and a rechargeable battery capable of being charged with the direct current power inputted from the direct current power input unit, to serve as a task priority changing unit that determines the operational priority of a charge monitoring task to be higher than the operational priorities of other tasks when the rechargeable battery is being charged with the direct current power inputted from the direct current power input unit, and that determines the operational priority of the charge monitoring task to be lower than the operational priority of at least one of the other tasks when the rechargeable battery is not being charged with the direct current power inputted from the direct current power input unit. 
     According to a further embodiment, there is provided a task control method performed by a printer including a direct current power input unit supplied with direct current power and a rechargeable battery capable of being charged with the direct current power inputted from the direct current power input unit, the printer further including a control unit and a storage unit, wherein a task priority changing unit includes instructions executed by the control unit such that the control unit determines the operational priority of a charge monitoring task to be higher than the operational priorities of other tasks when the rechargeable battery is being charged with the direct current power inputted from the direct current power input unit, and determines the operational priority of the charge monitoring task to be lower than the operational priority of at least one of the other tasks when the rechargeable battery is not being charged with the direct current power inputted from the direct current power input unit. 
     Certain embodiments of a portable printer, a program and a task control method will now be described with reference to the accompanying drawings. The printer of one embodiment is a thermal portable printer that stores therein a paper roll wound with a label paper having a plurality of labels adhesively bonded to a backing sheet and performs printing with a thermal head. 
     The general structure of a portable printer  101  is provided below.  FIG. 1  is a perspective view showing the outward appearance of a portable printer according to one embodiment, and  FIG. 2  is a perspective view showing the outward appearance of the portable printer whose cover is opened. 
     The outward appearance of the portable printer  101  is a rectangular parallelepiped shape. The housing  102  accommodates therein a print mechanism  300  (see  FIG. 4 ) for carrying out a printing function and a paper feeding function, and a rechargeable battery  270  (see  FIG. 4 ). In the present embodiment, a lithium-ion battery is used as the rechargeable battery  270 . The housing  102  has an internal structure capable of storing a paper roll PR wound with a label paper PT having a plurality of labels L (see  FIG. 2 ) bonded to a backing sheet. An opening  106  is located on the upper surface of the housing  102  so that the paper roll PR can be fed into the housing  102  through the opening  106 . A cover  107  is located at the opening  106 . The opening  106  is brought into an open state or a closed state by the opening or closing of the cover  107 . 
     A cover opening-closing sensor  50  (see  FIG. 4 ) for sensing the open state and the closed state of the cover  107  is provided in the housing  102 . The cover opening-closing sensor  50  is in some embodiments a micro-switch, which is a mechanical sensor. When the cover  107  is released from the housing  102  to thereby open the opening  106 , the cover opening-closing sensor  50  comes into an off-state in which no current flows. On the contrary, when the cover  107  covers the opening  106 , the cover opening-closing sensor  50  comes into an on-state in which current flows. The cover opening-closing sensor  50  is not limited to the micro-switch. It is possible to use, a contactless switch provided with a photo sensor or other switches as the cover opening-closing sensor  50 . 
     The cover  107  is attached to the inner side  108  of the housing  102  defining one side of the opening  106 . A slot through which to take out the printed label paper PT in a widthwise direction of the portable printer  101  is formed, with the cover  107  being closed, between the outer side  111 , which is the front end of the cover  107 , and the front side  109 , which is one side of the opening  106 . This slot serves as a paper outlet  110 . 
     A connector unit  103  having various connectors and a battery storage unit  104  for removably storing the rechargeable battery  270  are arranged on one side of the housing  102 . 
     The front side  109  of the housing  102  or the outer side  111  of the cover  107 , each defining the paper outlet  110 , is formed in a knife-edge shape to cut the label paper PT discharged from the paper outlet  110 . 
     A paper storage unit  105  capable of removably storing the paper roll PR is formed inside the housing  102 . The paper roll PR is stored in the paper storage unit  105  with a roll shaft oriented in a widthwise direction of the portable printer  101 . The paper roll PR is unwound by a platen  117  and conveyed toward the paper outlet  110  (see  FIG. 1 ). A thermal head  112  is arranged to be opposed to the platen  117 . 
     The thermal head  112  is removably mounted on a head bracket  115  arranged underneath the thermal head  112 . The head bracket  115  is fixed to the housing  102  to bias the thermal head  112  in the inner upper direction of the portable printer  101 . At the inner side of the portable printer  101 , a head cover  116  is arranged near the thermal head  112 . If necessary, the head cover  116  is mounted on the housing  102 , thereby biasing the thermal head  112  to prevent vibration thereof. 
     The thermal head  112  is configured to have a plurality of heating element arrays  114  arranged in rows having a specified density. As the heating element arrays  114  generate heat under the control of a head control unit  133  (see  FIG. 4 ), the thermal head  112  prints by heating the labels L of the label paper PT. Either, for example, a 203 dpi or 300 dpi thermal head may be selectively mounted on the head bracket  115 . 
     A driving gear  119  is arranged within the housing  102 . The driving gear  119  is turned by a drive power source, particularly a stepping motor  131  (see  FIG. 4 ) operating under the control of a motor control unit  134  (see  FIG. 4 ). 
     A paper pressing roller  118  is arranged near the platen  117  in the cover  107 . The platen  117  and the paper pressing roller  118  are rotatable about their rotation shafts extending in a widthwise direction of the portable printer  101 . 
     The platen  117  is arranged on the cover  107  in such a position that it can make contact with the heating element arrays  114  of the thermal head  112  when the cover  107  is closed. A driven gear  119   a  rotating together with the platen  117  is coupled to the left end of the platen  117  as seen from the front side of the portable printer  101 . 
     If the cover  107  is closed, the driven gear  119   a  meshes with the driving gear  119  and is driven by the driving gear  119 . The paper pressing roller  118  is coupled to the cover  107  in such a position that it can make contact with the head cover  116  when the cover  107  is closed. If the cover  107  is closed, the driven gear  119   a  attached to the cover  107  meshes with the driving gear  119 , thus rotationally driving the platen  117  connected to the driven gear  119   a . In the present embodiment, the driving gear  119  and the driven gear  119   a  make up a transmission  132  (see  FIG. 4 ). 
     In the present embodiment, the paper roll PR is arranged within the paper storage unit  105  in such a fashion that it can be attached or removed by a lever  122 . The paper roll PR is positioned between two guide fences  121 , where the space between the two guide fences  121  can be adjusted in conformity with the width of the paper roll PR. 
     As shown in  FIG. 3 , a label sensor  51  for detecting the positions of the labels L adhesively bonded to the backing sheet of the label paper PT is provided on the paper path, which connects the paper storage unit  105  and the thermal head  112 . More specifically, the label sensor  51  may be either a transmission-type sensor for detecting the gap between the labels L adhesively bonded to the backing sheet of the label paper PT or a reflection-type sensor for detecting the labels L adhesively bonded to the backing sheet of the label paper PT. 
     In the housing  102 , there is also arranged a direct current power input unit  210  to which direct current power is supplied from an external power source. A plug  404  of an AC adapter  400  is inserted into the direct current power input unit  210 , so as to supply direct current power to the portable printer  101 . 
     The AC adapter  400  is formed independently of the portable printer  101  and is inserted into an external commercial power socket to output direct current power. The AC adapter  400  includes a main body  401  provided with a direct current conversion circuit therein, a socket plug  402  attached to the main body  401 , a cable  403  through which direct current power is output and a cable plug  404 . The 100V AC inputted from the socket plug  402  is converted to 20V DC and then output to the cable plug  404  provided at the end of the cable  403 . In another embodiment, the portable printer may include an AC-DC converter within the housing  102 . 
     In addition to the general-purpose AC adapter, it is possible to use a car adapter (with input and output power of 12V), a DC-DC converter (with input power of 10 to 60V and output power of 20V) or the like as the device for supplying direct current power to the direct current power input unit  210 . 
     If the cable plug  404  is connected to the direct current power input unit  210 , direct current power is supplied to the portable printer  101 . Thus, the rechargeable battery  270  is brought into a rechargeable state. 
     In the housing  102 , there is also provided an operation part  150 . The operation part  150  includes a power switch  151 , a paper feeding button  152  provided for the user to instruct paper feeding, a pause button  153  provided for the user to pause paper feeding, an indicator  154  for notifying the user of the charging state of the rechargeable battery  270 , a liquid crystal display (LCD)  155  and a communication window  156 . In a nutshell, the portable printer  101  can perform data transmission and reception by infrared communication or other communication through the communication window  156  and a communication interface  140  (see  FIG. 5 ). Thus, the portable printer  101  is capable of receiving, e.g., print data, and storing them in a random access memory (RAM)  13  or a flash memory  14  (see  FIG. 5 ). 
     Next, the control system of the portable printer  101  is described.  FIG. 4  is a block diagram showing the control system of the portable printer. 
     As shown in  FIG. 4 , the print mechanism  300  of the portable printer  101  includes a head control unit  133  for outputting print control signals inclusive of a strobe signal and a print signal to the thermal head  112  and a motor control unit  134  for outputting a drive pulse signal to the stepping motor  131 . Further, a print control unit  135  controls all the printer parts, including the cover opening-closing sensor  50 , the label sensor  51 , the operation part  150  and the print mechanism  300 . 
     The print mechanism  300  of the portable printer  101  includes a print density detection unit  136  for detecting whether the thermal head  112  mounted on the head bracket  115  has a print density of 300 dpi or a print density of 203 dpi. 
       FIG. 5  is a block diagram showing the configuration of the print control unit  135 . As shown in  FIG. 5 , the print control unit  135  includes a CPU (central processing unit)  11  for performing various calculating processes to intensively control the respective parts. A RAM (random access memory)  13  and a non-volatile flash memory  14  are connected to the CPU  11  through a system bus  15 . 
     The flash memory  14  stores the operation program of the portable printer  101  and various kinds of setting information. The setting information stored in the flash memory  14  includes the priority of the processing operations of various tasks. The CPU  11  controls the respective parts by copying, into the random access memory  13 , the operation program stored in the flash memory  14  and executing the copied operation program. The operation program includes, e.g., the program for performing the task control processing which will be described below. 
     The RAM  13  temporarily stores various kinds of variable information. A partial area of the RAM  13  is used as a print buffer for extracting the print data (image data) to be printed on the labels L of the label paper PT. The print data refers to the data relating to the print object which is received from a host computer (not shown). The print data may be stored in the flash memory  14 . The host computer includes, e.g., a personal computer, a cellular phone and a handy terminal, and performs various calculating processes in response to the operation input made by the user. 
     A communication interface  140 , a display controller  141 , a key controller  142  and a sensor controller  143  are connected to the CPU  11  through a system bus  15 . Under the control of the CPU  11 , the display controller  141  controls the display (of, e.g., the remaining battery level, the radio wave receiving condition or the error message) displayed on the LCD  155  of the operation part  150 . Under the control of the CPU  11 , the key controller  142  controls the key input received from the power switch  151 , the paper feeding button  152  and the pause button  153  of the operation part  150 . Under the control of the CPU  11 , the sensor controller  143  controls the input from the sensors such as the cover opening-closing sensor  50  and the label sensor  51 . 
     The communication interface  140  is an interface for communicating with external devices such as the host computer. The communication interface  140  is formed of, e.g., an infrared communication tool such as IrDA or the like, a USB (Universal Serial Bus), a wireless LAN (Local Area Network), RESISTOR-232C and Bluetooth® and thus, it is capable of communicating with the communication interface provided in the host computer. 
     The portable printer  101  further includes a power control circuit  200  within the housing  102 . Responsive to the on/off operation of the power switch  151  of the operation part  150 , the power control circuit  200  software-controls the supply and cutoff of the power supplied from the external commercial power socket through the AC adapter  400  or the power supplied from the rechargeable battery  270 . As to the term “software-control,” it means that the supply and cutoff of the power is controlled by the control signal of the portable printer  101 . 
     The power control circuit  200  includes a direct current power input unit  210 , a voltage changing unit  220 , a power monitoring unit  230 , a power control unit  240 , a power cutoff unit  250 , a power source changeover unit  260  and a system power supply circuit  280  as a power supply unit. 
     The voltage changing unit  220  changes the voltage of the direct current power of a predetermined voltage range (e.g., 10V to 25V) inputted from the direct current power input unit  210  to a voltage suitable for use in the rechargeable battery  270  e.g., a voltage of 8.4V or 16.8V, which varies with the specification of the rechargeable battery  270 . Since a lithium-ion battery is used as the rechargeable battery  270  in the present embodiment, the rechargeable battery  270  performs its charging operation in a CC/CV charging method, namely by dropping the external DC voltage and charging in a constant current/constant voltage. 
     When performing the charging operation, the voltage changing unit  220  can set a long-lifespan mode for prolonging the battery lifespan, by varying the charging voltage and current or by adjusting the recharge threshold value. The power monitoring unit  230  monitors the voltage of the direct current power supplied from the direct current power input unit  210 . The power cutoff unit  250  serves to cut off the direct current power supplied from the direct current power input unit  210 , if the voltage of the direct current power detected by the power monitoring unit  230  falls outside a predetermined range (e.g., a range of 10V to 25V). The power source changeover unit  260  serves to change over the drive power fed to the print mechanism  300 , to power supplied from either the direct current power input unit  210  or the power supplied from the rechargeable battery  270 . 
     The power control unit  240  performs the following control with respect to the power cutoff unit  250  and the power source changeover unit  260 . 
     If the detection results of the power monitoring unit  230  show that the direct current power supplied from the direct current power input unit  210  falls within a predetermined range (10V to 25V), the power source changeover unit  260  is operated so that the direct current power supplied from the direct current power input unit  210  can flow to the voltage changing unit  220 . This allows the direct current power (8.4V) for recharging to be fed from the voltage changing unit  220  to the rechargeable battery  270 . In this state, the power supplied from the direct current power input unit  210  is also fed to the system power supply circuit  280 . 
     Upon receiving a print signal from the print control unit  135  in a state that the direct current power is supplied externally to the direct current power input unit  210 , the power control unit  240  operates the power source changeover unit  260  so that the drive power for the print mechanism  300  can be used as the power for the rechargeable battery  270 . According to the above description, if there is a print instruction, the power supplied from the direct current power input unit  210  to the print mechanism  300  is cut off. However, if the voltage supplied from the direct current power input unit  210  falls within the predetermined range, the power to the print control unit  135  is fed from the direct current power input unit  210 . 
     Even when there is no print instruction, the power control unit  240  operates the power source changeover unit  260  to feed the power from the rechargeable battery  270  to the system power supply circuit  280  if the voltage of the direct current power detected by the power monitoring unit  230  is lower than the voltage of the rechargeable battery  270 . 
     The system power supply circuit  280  feeds the power to each part of the print mechanism  300  through the print control unit  135 . The power within the range of allowable voltage is applied to the thermal head  112  of the print mechanism  300 . In other words, when the portable printer  101  performs printing, the power supplied from the direct current power input unit  210  is cut off by the power cutoff unit  250  but the power from the rechargeable battery  270  is fed to the thermal head  112 . This means that a voltage greater than the allowable voltage of the thermal head  112  is not fed to the thermal head  112 . 
     The system power supply circuit  280  feeds the power (of, e.g., 5V, 3.3V or 1.5V in voltage) needed to drive the print control unit  135 . Thus, in the system power supply circuit  280 , the operation input voltages to be fed to each part are set to ensure that the respective parts can properly operate within the range of the voltage of the external direct current power and the rechargeable battery  270 . 
     The system power supply circuit  280  performs the on/off control of each power supply system that is driven by the direct current power supplied from the rechargeable battery  270  and the direct current power input unit  210 . In other words, the system power supply circuit  280  allows the direct current power to be fed from the direct current power input unit  210  to the print control unit  135  if the direct current power input unit  210  is supplied with the direct current power. In contrast, the system power supply circuit  280  allows the direct current power to be fed from the rechargeable battery  270  to the print control unit  135  if the direct current power input unit  210  is not supplied with the direct current power. 
     When the power control unit  240  allows the direct current power to be fed from the rechargeable battery  270  to the print control unit  135 , the system power supply circuit  280  feeds the direct current power to the print mechanism  300  via the print control unit  135 . 
     In addition to controlling the print mechanism  300 , the print control unit  135  acquires information delivered from the voltage changing unit  220  and the system power supply circuit  280  during the power supplying period and if the voltage changing unit  220  and the system power supply circuit  280  are in a condition where they can be charged, transmits charge startup instructions to the power control unit  240 . 
     The print control unit  135  sets the portable printer  101  in different status modes depending on the circumstances. The status modes include, for example, a standby mode in which the thermal head  112  can perform printing at once, a sleep mode in which the system stays in an energy-saving state to reduce power consumption, a print mode in which printing is performed by the thermal head  112 , a charge mode in which the rechargeable battery  270  is charged and a long-lifespan charge mode in which charging is performed at a low voltage without shortening the lifespan of the rechargeable battery  270 . 
     Transition to the respective modes is controlled in the following manner. 
     When the portable printer  101  is driven by the rechargeable battery  270 , it goes into sleep mode if it remains in standby mode for a predetermined amount of time. In the sleep mode, the power supply to unnecessary functional parts is cut off, but the communication interface  140  stays in a standby state. The sleep mode comes back to the standby mode if there is a need to operate the print mechanism  300  or if signal transmission or reception occurs in the communication interface  140  during the sleep mode. 
     When the portable printer  101  is supplied with external direct current power, it goes into standby mode without going into sleep mode. This makes it possible to rapidly start up the print mode. In the standby mode, the communication interface  140  is kept in a standby state and the voltage changing unit  220  controls the charging operation of the rechargeable battery  270 . 
     In the portable printer  101  described above, if the paper roll PR is put into the paper storage unit  105  and the label paper PT is pulled out and then the cover  107  is closed, the pulled-out label paper PT is placed between the thermal head  112  and the platen  117  and between the head cover  116  and the paper pressing roller  118 . In case it goes into the print mode under the control of the print control unit  135  with the above state, the label paper PT is conveyed from the paper roll PR toward the paper outlet  110  through the thermal head  112  if the stepping motor  131  is driven by the control of the motor control unit  134 . The thermal head  112  causes the heating element arrays  114  to generate heat under the control of the head control unit  133 , thereby printing specific content on the labels L of the conveying label paper PT. 
     Next, the task control processing performed by the CPU  11  according to the program stored in the flash memory  14  will be described with reference to the function block diagram shown in  FIG. 6  and the flowchart illustrated in  FIG. 7 . 
     The program executed in the portable printer  101  of the present embodiment has a module configuration including a task priority changing unit  10  shown in  FIG. 6 . In the actual hardware, as the CPU  11  reads the program from the flash memory  14  and executes the same, the individual parts mentioned above are loaded onto the RAM  13  and thus, the task priority changing unit  10  is generated on the RAM  13 . 
     As illustrated in  FIG. 7 , when the portable printer  101  goes into the sleep mode to keep the system in an energy-saving state for reducing the power consumption, the task priority changing unit  10  determines whether direct current power is supplied from outside the portable printer  101  to the direct current power input unit  210  (act A 1 ). 
     If it is determined that the direct current power is not supplied from outside the portable printer  101  to the direct current power input unit  210  (if “No” in act A 1 ), the rechargeable battery  270  is not charging. Therefore, the task priority changing unit  10  reduces the priority of the charge monitoring task for monitoring the charging state of the rechargeable battery  270 , (act A 2 ). Therefore, when the operational priority of the charge monitoring task is lower than the operational priority of, e.g., a roaming task for searching a base station through the communication interface  140 , i.e., a wireless LAN, mounted on the portable printer  101 , the roaming task may be performed preferentially. Since the processing speed of the CPU  11  is slowed in sleep mode, it takes more time in sleep mode to perform the roaming task than in a normal operation period. However, it is sufficient for the CPU  11  to perform the roaming task in sleep mode. In some embodiments, when operating the portable printer  101  with the rechargeable battery  270 , no overcharging occurs even if the charge monitoring is delayed. 
     On the other hand, even though the operational priority of the charge monitoring task has been reduced, the task priority changing unit  10  increases the operational priority of the charge monitoring task on the rechargeable battery  270  (act A 3 ) if the socket plug  404  of the AC adapter  400  inserted into a commercial power socket is connected to the direct current power input unit  210  so that the direct current power can be supplied to the portable printer  101  (if “Yes” in act A 1 ). Inasmuch as the portable printer  101  is kept immovable while the rechargeable battery  270  is charged, the possibility of performing the roaming task at that time remains low. This means that no problem arises even if the roaming task is not performed preferentially. 
     As used in this application, entities for executing the actions can refer to a computer-related entity, either hardware, a combination of hardware and software, software, or software in execution. For example, an entity for executing an action can be, but is not limited to being, a process running on a processor, a processor, an object, an executable, a thread of execution, a program, and a computer. By way of illustration, both an application running on an apparatus and the apparatus can be an entity. One or more entities can reside within a process and/or thread of execution and an entity can be localized on one apparatus and/or distributed between two or more apparatuses. 
     The program for realizing the functions can be recorded in the apparatus, can be downloaded through a network to the apparatus and can be installed in the apparatus from a computer readable storage medium storing the program therein. A form of the computer readable storage medium can be any form as long as the computer readable storage medium can store programs and is readable by the apparatus such as a disk type ROM and a Solid-state computer storage media. The functions obtained by installation or download in advance in this way can be realized in cooperation with an OS(Operating System) or the like in the apparatus. 
     According to the present embodiment described above, the operational priority of the charge monitoring task for monitoring the charging state of the rechargeable battery  270  is kept higher than the operational priorities of other tasks when the rechargeable battery  270  is charged with the direct current power inputted from the direct current power input unit  210 . In contrast, the operational priority of the charge monitoring task is kept lower than the operational priority of at least one of other tasks when the rechargeable battery  270  is not charging. In some embodiments it is possible to preferentially perform other tasks than the charge monitoring task when the rechargeable battery  270  is not charging (e.g., when the printer is in operation). More specifically, the charge monitoring task in some embodiments is of paramount importance when the rechargeable battery  270  is charging, but is not so important when the rechargeable battery  270  is not charging (e.g., when the printer operates). By keeping the priorities of other tasks (e.g., a roaming task for searching a base station through a wireless LAN) higher than the priority of the charge monitoring task, it is possible in some embodiments to preferentially perform other tasks than the charge monitoring task (e.g., a roaming task for searching a base station through a wireless LAN), which have an importance when the rechargeable battery  270  is not charging (e.g., during the printer driving period). 
     In particular, if the priority of the roaming task is lower than that of the charge monitoring task in the sleep mode in which the system is kept in an energy-saving state to reduce power consumption, where the rechargeable battery  270  is not charging, the roaming (i.e., searching the base station) becomes delayed due to the reduced processing speed of a CPU and, consequently, the wireless communication may be interrupted halfway. This problem can be solved by preferentially performing the roaming task. 
     Although the program executed in the portable printer  101  of the present embodiment is preliminarily incorporated in the flash memory  14  according to the description made above, the present embodiment is not limited thereto. Alternatively, the program executed in the portable printer  101  of the present embodiment may be provided by recording the same in a computer-readable recording medium such as a CD-ROM, a flexible disk (FD), a CD-R or a DVD (Digital Versatile Disk) as an installable or executable file. 
     In addition, the program executed in the portable printer  101  of the present embodiment may be stored in a computer connected to a network such as the Internet or the like so that the program can be down-loaded from the computer via the network. Moreover, the program executed in the portable printer  101  of the present embodiment may be provided or disseminated via a network such as the Internet or the like. 
     While certain embodiments have been described above, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel printer, the novel program and the novel task control method described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the printer, the program and the task control method described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.