Patent Publication Number: US-8534938-B2

Title: Printer and method for switching between standard mode and liner-less mode

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No, 2010-034017, filed on Feb. 18, 2010, the entire contents of which are incorporated herein by reference. 
     FIELD 
     Embodiments described herein relate generally to a printer for printing a backing sheet-attached label or a liner-less label and a printing method. 
     BACKGROUND 
     In general, a printer for use in printing a backing sheet-attached label and a liner-less label prints at a constant printing speed either when printing a backing sheet-attached label discharged from a roll of backing sheet-attached labels with an interlaid backing sheet or when printing a liner-less label discharged from a roll of liner-less labels with an interlaid adhesive surface. 
     In the roll of liner-less labels, the liner-less labels are wound in a roll shape with an adhesive surface on one side of the liner-less label. Therefore, as compared with the roll of backing sheet-attached labels in which the backing sheet-attached labels are wound in a roll shape with a backing sheet having no adhesiveness, more force is required in stripping the liner-less label from the roll of liner-less labels. 
     As described above, the printer of related art performs printing at a constant printing speed either when printing the backing sheet-attached label discharged from the roll of backing sheet-attached labels or when printing the liner-less labels discharged from the roll of liner-less labels. In this case, a problem is posed in that a motor load required for driving a roller grows higher when discharging the liner-less label from the roll of liner-less labels. Particularly, in a portable printer with a motor driven by electric power supplied from a battery, battery consumption becomes greater if the motor load grows higher. Thus, the portable printer cannot be used for a long period of time. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a portable printer according to one embodiment. 
         FIG. 2  is a perspective view of the portable printer whose cover is open. 
         FIG. 3  is a schematic diagram illustrating a label conveying path. 
         FIG. 4  is a block diagram of a control system of the portable printer. 
         FIG. 5  is a block diagram showing the configuration of a print control unit. 
         FIG. 6  is a block diagram of a portable printer according to one embodiment. 
         FIG. 7  is illustrates a strobe signal indicative of the heating time of a thermal head within a single-dot printing period. 
         FIG. 8  is a flowchart illustrating a process to control the rotation speed of a platen roller. 
         FIG. 9  is a flowchart illustrating a process to back-feed a backing sheet-attached label or a liner-less label. 
     
    
    
     DETAILED DESCRIPTION 
     According to one embodiment, a printer includes a motor and a roller turned by the motor to discharge a backing sheet-attached label from a roll wound with the backing sheet-attached label, or discharge a liner-less label from a roll wound with the liner-less label with an adhesive surface on one side of the liner-less label. The printer further includes a print unit to perform printing on the backing sheet-attached label or the liner-less label discharged from the roll, and a switching unit to switch the printer to any one of a standard mode in which the print unit performs printing on the backing sheet-attached label and a liner-less mode in which the print unit performs printing on the liner-less label. Further, the printer includes a control unit to control the operation of the motor in response to the switching of the printer to any one of the standard mode and the liner-less mode. 
     Certain embodiments of a printer, a printing method and a recording medium having a printing program will now be described in detail with reference to the accompanying drawings. In one embodiment, description will be made with respect to an example in which the printer, the printing method and the printing program are applied to a portable thermal printer that contains a roll of backing sheet-attached labels or a roll of liner-less labels and performs printing by heating the print surface of a backing sheet-attached label or a liner-less label with a thermal head. 
     The schematic structure of a portable printer  101  will be described with reference to  FIGS. 1 to 3 .  FIG. 1  is a perspective view of the portable printer  101 .  FIG. 2  is a perspective view of the portable printer  101  whose cover is open.  FIG. 3  is a schematic diagram illustrating a label conveying path. 
     The portable printer  101  has a rectangular parallelepiped shape. The portable printer  101  includes a print mechanism  300  (see  FIG. 4 ) to carry out a printing function and a paper feeding function, a rechargeable battery  270  (see  FIG. 4 ) used as a power source and a housing  102  to accommodate the print mechanism  300  and the rechargeable battery  270  therein. In the present embodiment, a lithium-ion battery may be used as the rechargeable battery  270 . The housing  102  has an internal structure to store a paper roll PR wound with a backing sheet-attached label having a label adhesively bonded to a backing sheet or a paper roll PR wound with a liner-less label having an adhesive surface, e.g., a glue surface. An opening  106  is defined on the upper surface of the housing  102  so that the paper roll PR can be put in the housing  102  through the opening  106 . A cover  107  is pivotally arranged in the opening  106 . The cover  107  may open or close, which makes the opening  106  in an open state or a close state. 
     Further, the housing  102  includes a cover opening-closing sensor  50  (see  FIG. 4 ) for detecting the open state and the close state of the cover  107 . The cover opening-closing sensor  50  may include a micro-switch, which may in some embodiments be a mechanical sensor. When the cover  107  is opened from the housing  102  to make the opening  106  open, the cover opening-closing sensor  50  comes into an off-state in which no electric current flow. On the other hand, if the cover  107  covers the opening  106 , the cover opening-closing sensor  50  comes into an on-state in which an electric current flows. The cover opening-closing sensor  50  is not limited to the above-mentioned micro-switch, but may include a contactless switch provided with a photo sensor or other switches. 
     The cover  107  is attached to an inner side  108  of the housing  102  defining one side of the opening  106 . When the cover  107  is in a closed state, a slot for discharging a printed backing sheet-attached label or a printed liner-less label is formed between the outer side  111 , i.e., the front end of the cover  107  and the front side  109 , i.e., one side of the opening  106 . This slot extends in the transverse direction of the portable printer  101  and serves as a paper outlet  110 . 
     On one lateral surface of the housing  102 , there are arranged a connector portion  103  including a variety of connectors and a battery storage portion  104  to detachably enclose the rechargeable battery  270 . 
     The front side  109  of the housing  102  or the outer side  111  of the cover  107 , respectively defining the paper outlet  110 , has a sharp-edged shape to cut the backing sheet-attached label or the liner-less label discharged from the paper outlet  110 . 
     The housing  102  includes a paper storage portion  105  to detachably enclose the paper roll PR. The paper roll PR is enclosed in the paper storage portion  105  with a roll shaft oriented in the transverse direction of the portable printer  101 . The platen roller  117  is turned by the stepping motor  131  (see  FIG. 4 ) used as a drive power source, thereby discharging the backing sheet-attached label or the liner-less label from the paper roll PR stored in the paper storage portion  105  and conveying the discharged label toward the paper outlet  110  (see  FIG. 1 ). The platen roller  117  is arranged to be opposed to the thermal head  112 , which will be described below. The platen roller  117  can be turned by the stepping motor  131  (see  FIG. 4 ) used as a drive power source in the direction opposite to the direction in which the backing sheet-attached label or the liner-less label is discharged from the paper roll PR, thereby back-feeding the backing sheet-attached label or the liner-less label that has already reached the paper outlet  110 . 
     The thermal head  112  is detachably mounted to a head bracket  115 , which is arranged in the lower portion. The head bracket  115  is fixed to the housing  102  to abut against the thermal head  112  in the upper inner direction of the portable printer  101 . A head cover  116  is arranged near the thermal head  112  at the inner side of the portable printer  101  from the thermal head  112 . The head cover  116  is selectively mounted to the housing  102 , thereby abutting against the thermal head  112  to prevent the thermal head  112  from vibrating. 
     The thermal head  112  includes a plurality of heating elements  114  arranged in a row with a certain density. As the heating elements  114  generate heat under the control of a head control unit  133  (see  FIG. 4 ), the thermal head  112  performs printing by heating the print surface of the backing sheet-attached label or the liner-less label. The thermal head  112  is detachably mounted to the head bracket  115 . The thermal head  112  with e.g., 200 dpi or 300 dpi, may be selectively mounted to the head bracket  115 . 
     As shown in  FIG. 3 , the paper outlet  110  is arranged at the downstream side of the thermal head  112  along the discharging direction of the backing sheet-attached label or the liner-less label. 
     A driving gear  119  is arranged within the housing  102 . The driving gear  119  is turned by a stepping motor  131  (see  FIG. 4 ) used as a drive power source, which is operated under the control of a motor control unit  134  (see  FIG. 4 ). 
     A paper pressing roller  118  is arranged near the platen roller  117  in the cover  107 . The platen roller  117  and the paper pressing roller  118  are rotatable along their rotation axes extending in the transverse direction of the portable printer  101 . 
     The platen roller  117  is arranged at a position in the cover  107 , where it can make contact with the heating elements  114  of the thermal head  112  when the cover  107  is in the closed state. The platen roller  117  is coupled with a driven gear  119   a  on the left side of the platen roller  117 , when viewed from the front side of the printer  101 , so as to rotate together. 
     The driven gear  119   a  is engaged with the driving gear  119  so as to be driven by the driving gear  119 , when the cover  107  comes into the closed state. The paper pressing roller  118  is coupled to the cover  107  at such a position that it can make contact with the head cover  116  when the cover  107  is in the closed state. When the cover  107  is closed, the driven gear  119   a  mounted to the cover  107  is engaged with the driving gear  119 , thus rotationally driving the platen roller  117  coupled to the driven gear  119   a . In the present embodiment, the driving gear  119  and the driven gear  119   a  serve as a transmission  132  (see  FIG. 4 ). 
     In the present embodiment, the paper roll PR is arranged within the paper storage portion  105  in such a fashion that it can be attached or detached by a lever  122 . The paper roll PR is positioned between two guide fences  121 . The space between two guide fences  121  can be adjusted in accordance with the width of the paper roll PR. 
     The housing  102  includes a direct current (DC) power input part  210  for inputting DC power from an external power source. A plug  404  of an AC adapter  400  is inserted into the DC power input part  210 , so that DC power is supplied to the portable printer  101 . 
     The AC adapter  400  is provided separately from the portable printer  101 . The AC adapter  400  is inserted into an external commercial power socket to output DC power from the plug  404 . The AC adapter  400  includes a main body  401  provided with a DC conversion circuit, a socket plug  402  attached to the main body  401 , a cable  403  to output DC power, and a cable plug  404 . The AC adaptor  400  converts the electric power of, e.g., AC 100V, inputted from the socket plug  402  to the electric power of e.g., DC 20V, which is then outputted to the cable plug  404  provided at the tip end of the cable  403 . 
     Besides a general-purpose AC adapter, a car adapter (with input power and output power of 12V), a DC-DC converter (with input power of 10V to 60V and output power of 20V) may be used as the device for supplying DC power to the DC power input part  210 . If the cable plug  404  is connected to the DC power input part  210 , DC power is supplied to the portable printer  101 . This brings the rechargeable battery  270  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  for allowing a user to instruct paper feeding, and a pause button  153  for allowing a user to instruct temporary stoppage of the paper feeding. The operation part  150  further includes an indicator  154  to notify the user of the charge state of the rechargeable battery  270 , a liquid crystal display (LCD)  155 , and a communication window  156 . The operation part  150  further includes a switching unit  157  enabling a user to perform a switching operation to a standard mode to print on a backing sheet-attached label or a liner-less mode to print on a liner-less label. In general, the portable printer  101  may perform data transmission and reception by, e.g., infrared communication through the communication window  156  and the communication interface  140  (see  FIG. 5 ). For example, the portable printer  101  may receive and store print data in a RAM (random access memory)  13  or a flash memory  14  (see  FIG. 5 ). 
     In the following, the control system of the portable printer  101  will be described.  FIG. 4  is a block diagram of a control system of the portable printer  101 . 
     As shown in  FIG. 4 , the print mechanism  300  of the portable printer  101  includes a head control unit  133  to output print control signals including a strobe signal and a print signal to the thermal head  112  and a motor control unit  134  to output a drive pulse signal to the stepping motor  131 . The print control unit  135  controls all components of the printer, including the cover opening-closing sensor  50 , 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  to detect whether the thermal head  112  mounted to the head bracket  115  has a print density of 200 dpi or 300 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  to perform various kinds of arithmetic processing to centrally control the respective components. A RAM  13  and a flash memory  14 , i.e., a non-volatile memory capable of keeping stored contents despite interruption of electric power, are connected to the CPU  11  through a system bus  15 . 
     The flash memory  14  stores operation programs and a variety of setting information of the printer  101 . The CPU  11  deploys the operation programs stored in the flash memory  14  to the working area of the RAM  13 , and executes the operation programs to control each component. The operation programs stored in the flash memory  14  includes, e.g., a program used to perform the control processing of the rotation speed of the platen roller  117  or the back-feed control processing of the backing sheet-attached label or the liner-less label. In addition, the flash memory  14  stores a rotation speed table and a back-feed length table respectively used in the control processing of the rotation speed of the platen roller  117  and in the back-feed control processing of the backing sheet-attached label or the liner-less label. 
     In this embodiment, the rotation speed table refers to a table in which the rotation speeds of the platen roller  117  are associated with the standard mode and the liner-less mode when printing the backing sheet-attached label or the liner-less label with the thermal head  112  in the respective modes. The rotation speed of the platen roller  117  associated with the liner-less mode is slower than that associated with the standard mode. 
     The back-feed length table refers to a table in which the lengths of the backing sheet-attached label or the liner-less label back-fed to the paper roll PR (hereinafter referred to as “back-feed length”) are respectively associated with the standard mode and the liner-less mode. The back-feed length (e.g., 5 mm) associated with the liner-less mode is shorter than the back-feed length (e.g., 10 mm) associated with the standard mode. 
     The RAM  13  temporarily stores various kinds of variable information. A partial area of the RAM  13  is used as a print buffer to which the print data (image data) to be printed on the backing sheet-attached label or the liner-less label are deployed. The print data refers to the print object data 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 or a handheld terminal and executes various kinds of arithmetic processing in response to a user&#39;s operational input. 
     A communication interface  140 , a display controller  141 , a key controller  142  and a sensor controller  143  are connected to the CPU  11  through the system bus  15 . Under the control of the CPU  11 , the display controller  141  controls the display (e.g., a remaining battery level, radio wave reception conditions or error messages) of the liquid crystal display  155  of the operation part  150 . Under the control of the CPU  11 , the key controller  142  controls the key inputs 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 inputs received from various sensors such as the cover opening-closing sensor  50  and the like. 
     The communication interface  140  refers to an interface configured to perform communication with the external devices such as the host computer and the like. The communication interface  140  may include an infrared communication tool such as an IrDA, a USB (Universal Serial Bus), a wireless LAN (Local Area Network), a RS-232C and Bluetooth (registered trademark). The communication interface  140  may communicate with a communication interface provided in the host computer. 
     The portable printer  101  further includes a power control circuit  200  arranged 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  performs software-control of the supply and cutoff of the electric power supplied from the external commercial power socket through the AC adapter  400  or the electric power supplied from the rechargeable battery  270  to the respective parts of the print mechanism  300 . The term “software-control” refers to controlling the supply and cutoff of the electric power based on the control signals of the portable printer  101 . 
     The power control circuit  200  includes a DC power input part  210 , a voltage converting unit  220 , a power monitoring unit  230 , a power control unit  240 , a power cutoff unit  250 , a power source switching unit  260  and a system power supply circuit  280  as a power supply unit. 
     The voltage converting unit  220  converts the voltage of the DC power from the DC power input unit  210  in a certain voltage range (e.g., 10V to 25V) to a voltage appropriate for recharging the rechargeable battery  270  (e.g., a voltage of 8.4V or 16.8V, which varies depending on the specification of the rechargeable battery  270 ). In one embodiment, the rechargeable battery  270  is a lithium-ion battery. The rechargeable battery  270  performs its recharging operation in a CC/CV recharging method, namely in a constant current and constant voltage recharging method, by dropping the DC voltage supplied from outside. 
     When the recharging operation is performed, the voltage converting unit  220  may set a long-lifespan mode for prolonging the battery lifespan by varying the recharging voltage and current or by adjusting the recharge threshold value. The power monitoring unit  230  monitors the voltage of the DC power from the DC power input unit  210 . The power cutoff unit  250  cuts off the DC power from the DC power input unit  210 , if the voltage of the DC power detected by the power monitoring unit  230  falls outside a predetermined range (e.g., a range of 10V to 25V). The power source switching unit  260  switches the power supplied to the system power supply circuit  280 , to the power supplied from the DC power input unit  210  or the power supplied from the rechargeable battery  270 . 
     The power control unit  240  performs the control of the power cutoff unit  250  and the power source switching unit  260 , as described below. If the power monitoring unit  230  detects that the DC power supplied from the DC power input unit  210  falls within a predetermined range (e.g., 10V to 25V), the power source switching unit  260  operates to allow the DC power from the DC power input unit  210  to flow into the voltage converting unit  220 . The voltage converting unit  220  supplies the DC power for recharging (e.g., 8.4V) to the rechargeable battery  270 . Similarly, the DC power from the DC power input unit  210  also flows into the system power supply circuit  280 . 
     Upon receiving a print signal from the printer control unit  135  when the DC power is supplied from outside to the DC power input unit  210 , the power control unit  240  operates the power source switching unit  260  to supply the power of the rechargeable battery  270  to the drive power for the print mechanism  300 . Thereby, when a print instruction is received, the power supplied from the DC power input unit  210  to the print mechanism  300  is cut off. However, if the voltage of the DC power supplied from the DC power input unit  210  falls within a predetermined range, the power may be supplied from the DC power input unit  210  to the printer control unit  135 . 
     Even when no print instruction is received, if the voltage of the DC power detected by the power monitoring unit  230  is lower than the voltage of the rechargeable battery  270 , the power control unit  240  operates the power source switching unit  260  to supply the power from the rechargeable battery  270  to the system power supply circuit  280 . 
     The system power supply circuit  280  feeds the electric power to the respective parts of the print mechanism  300  through the print control unit  135 . The electric power within the allowable range of voltage is applied to the thermal head  112  of the print mechanism  300 . In other words, when the printer  101  prints, the electric power cutoff unit  250  cuts off the electric power supplied from the DC power input unit  210 , and the power source switching unit  260  allows the electric power from the rechargeable battery  270  to supply to the thermal head  112 , so that a voltage greater than the allowable voltage is not supplied to the thermal head  112 . 
     The system power supply circuit  280  supplies the electric power (of, e.g., 5V, 3.3V or 1.5V) required to drive the print control unit  135 . In the system power supply circuit  280 , the operation input voltages to be fed to the respective parts or units are set to ensure that the respective parts or units can properly operate within the range of the voltage of the external DC power and the rechargeable battery  270 . 
     The system power supply circuit  280  performs the on/off control of the individual power systems that are driven by the DC power supplied from the rechargeable battery  270  and the DC power input unit  210 . In other words, if the DC power input unit  210  is supplied with DC power, the system power supply circuit  280  allows DC power to flow from the DC power input unit  210  to the printer control unit  135 . In contrast, if the DC power input unit  210  is not supplied with DC power, the system power supply circuit  280  allows DC power to flow from the rechargeable battery  270  to the printer control unit  135 . 
     If the power control unit  240  allows DC power to flow from the rechargeable battery  270  to the printer control unit  135 , the system power supply circuit  280  supplies the DC power to the print mechanism  300  via the printer control unit  135 . 
     In addition to performing the control of the print mechanism  300 , the print control unit  135  acquires information delivered from the voltage converting unit  220  and the system power supply circuit  280  during the power supplying period and transmits a charge startup instruction to the power control unit  240  if the voltage converting unit  220  and the system power supply circuit  280  are kept in a chargeable condition. 
     Depending on the circumstances, the print control unit  135  sets the portable printer  101  in different status modes. Examples of the status modes include a standby mode in which printing is immediately performed by the thermal head  112 , 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 driven by the rechargeable battery  270 , the portable printer  101  goes into the sleep mode after a specified time has lapsed from the standby mode. In the sleep mode, unnecessary power supplied to some functional parts is cut off and the communication interface  140  alone is ready to receive signals in a standby state. The sleep mode comes back to the normal 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. 
     While being supplied with external DC power, the portable printer  101  does not enter the sleep mode but stays in the normal standby mode. This allows the printer to readily start up the print mode. In the standby mode, the communication interface  140  is ready to receive signals in a standby state and the voltage converting unit  220  performs the charge control of the rechargeable battery  270 . 
     In the portable printer  101  as described above, if the backing sheet-attached label or the liner-less label is discharged from the paper roll PR stored in the paper storage portion  105  and if the cover  107  is closed, the backing sheet-attached label or the liner-less label is interposed between the thermal head  112  and the platen roller  117  and also interposed between the head cover  116  and the paper pressing roller  118 . If printing starts in this state under the control of the print control unit  135  and if the stepping motor  131  is driven by the control of the motor control unit  134 , the backing sheet-attached label or the liner-less label is conveyed from the paper roll PR toward the paper outlet  110  via the thermal head  112 . The thermal head  112  causes the heating elements  114  to generate heat under the control of the head control unit  133 , thereby printing a certain content on the backing sheet-attached label or the liner-less label being conveyed. 
     The functions executed and implemented by the CPU  11  according to the program stored in the flash memory  14  of the print control unit  135  will be described with reference to the block diagram illustrated in  FIG. 6 .  FIG. 6  is a block diagram of the portable printer  101 . 
     The program executed in the portable printer  101  of the present embodiment includes a module configuration containing parts or units as illustrated in  FIG. 6  to switching unit  10 , a control unit  20  and an adjustment unit  30 ). In the actual hardware, the CPU  11  reads the program from the flash memory  14  and executes the same, whereby the respective parts or units are loaded to the RAM  13  so that the respective parts or units (the switching unit  10 , the control unit  20  and the adjustment unit  30 ) can be created in the RAM  13 . 
     The switching unit  10  serves to switch the portable printer  101  to the standard mode or the liner-less mode in response to the switching operation inputted through the switching unit  157 . Thus, the user can selectively switch the portable printer  101  to the standard mode or the liner-less mode depending on whether the paper roll PR loaded into the portable printer  101  is the roll of backing sheet-attached labels or the roll of liner-less labels. 
     In the present embodiment, while the portable printer  101  is switched to the standard mode or the liner-less mode in response to the switching operation inputted through the switching unit  157 , the configuration of the portable printer  101  may not be limited thereto. For example, if a touch panel for detecting location of a touch is arranged in the liquid crystal display  155 , an object enabling a switching operation to the standard mode or the liner-less mode may be displayed on the liquid crystal display  155 . Also, the configuration of the switching unit  157  is not limited to a mechanical button but may be implemented by any type of switching configurations (a lever, electrical switch etc.) employed in the related art. Responsive to the switching operation of the object to the standard mode or the liner-less mode, the switching unit  10  may switch the portable printer  101  to the standard mode or the liner-less mode. Alternatively, the switching unit  10  may determine whether the paper roll PR stored in the paper storage portion  105  is the roll of backing sheet-attached labels or the roll of liner-less labels and, depending on the result of determination, may switch the portable printer  101  to the standard mode or the liner-less mode. As a further alternative, the switching unit  10  may switch the portable printer  101  to the standard mode or the liner-less mode according to a command transmitted from a host computer (not shown). 
     The control unit  20  controls the operation of the stepping motor  131  through the motor control unit  134  in response to the switching operation to the standard mode or the liner-less mode performed by the switching unit  10 . For example, the control unit  20  performs control in such a fashion that the rotation speed of the platen roller  117  in the liner-less mode is lower than that in the standard mode. By doing so, the torque of the platen roller  117  when discharging the liner-less label from the paper roll PR may be set to be greater than the torque of the platen roller  117  when discharging the backing sheet-attached label from the paper roll PR. This may reduce the load applied to the stepping motor  131  when stripping the liner-less label from the paper roll PR to print on the liner-less label. 
     More specifically, if the portable printer  101  is switched to the standard mode by the switching unit  10 , the control unit  20  determines the rotation speed associated with the standard mode in the rotation speed table stored in the flash memory  14  and sets the determined rotation speed to be the rotation speed of the platen roller  117  in the standard mode. Then, the control unit  20  determines a drive pulse period T according to the determined rotation speed and causes the motor control unit  134  to output a drive pulse signal having the determined period T to the stepping motor  131 . 
     On the other hand, if the portable printer  101  is switched to the liner-less mode by the switching unit  10 , the control unit  20  determines the rotation speed associated with the liner-less mode in the rotation speed table stored in the flash memory  14  and sets the determined rotation speed to be the rotation speed of the platen roller  117  in the liner-less mode. Then, the control unit  20  determines a drive pulse period T (longer than the drive pulse period T of the drive pulse signal outputted to the stepping motor  131  when the portable printer  101  is switched to the standard mode by the switching unit  10 ) according to the determined rotation speed and causes the motor control unit  134  to output a drive pulse signal having the determined period T to the stepping motor  131 . 
     In addition, the control unit  20  is configured to ensure that the back-feed length of the liner-less label being back-fed to the thermal head  112  is shorter than the back-feed length of the backing sheet-attached label being back-fed to the thermal head  112 . 
     More specifically, if the portable printer  101  is switched to the standard mode by the switching unit  10 , the control unit  20  determines the back-feed length associated with the standard mode in the back-feed length table stored in the flash memory  14  and sets the determined back-feed length to be the back-feed length in the standard mode. According to the determined back-feed length, the control unit  20  determines the time period for which the drive pulse signal is to be outputted from the motor control unit  134  to the stepping motor  131  and causes the motor control unit  134  to output the drive pulse signal to the stepping motor  131  for the determined time period. 
     On the other hand, if the portable printer  101  is switched to the liner-less mode by the switching unit  10 , the control unit  20  determines the back-feed length associated with the liner-less mode in the back-feed length table stored in the flash memory  14  and sets the determined back-feed length to be the back-feed length in the liner-less mode. According to the determined back-feed length, the control unit  20  determines the time period for which the drive pulse signal is to be outputted from the motor control unit  134  to the stepping motor  131  (shorter than the time period for which the drive pulse signal is to be outputted from the motor control unit  134  to the stepping motor  131  when the portable printer  101  is switched to the standard mode by the switching unit  10 ) and causes the motor control unit  134  to output the drive pulse signal to the stepping motor  131  for the determined time period. 
     The rotation speed of the platen roller  117  when back-feeding the liner-less label to the thermal head  112  in the liner-less mode is set equal to the rotation speed of the platen roller  117  when back-feeding the backing sheet-attached label to the thermal head  112  in the standard mode. That is, the drive pulse period T of the drive pulse signal outputted to the stepping motor  131  when back-feeding the liner-less label to the thermal head  112  is set equal to the drive pulse period T of the drive pulse signal outputted to the stepping motor  131  when back-feeding the backing sheet-attached label to the thermal head  112 . 
     In general, In the portable printer  101 , after cutting the backing sheet-attached label or the liner-less label printed, the backing sheet-attached label or the liner-less label positioned at the paper outlet  110  may be back-fed to the thermal head  112  so that the subsequent printing on the backing sheet-attached label or the liner-less label can be performed without leaving a gap with respect to the previously printed portion. In the printer of related art, the back-feed distance of the liner-less label is set equal to the back-feed distance of the backing sheet-attached label. In this case, as the back-feed length is increased, the resilience of the liner-less label is reduced and thus tends to be bent. This means that a paper jam is highly likely to occur. 
     With the present embodiment, however, the liner-less label may be back-fed without causing that paper jam by the bending of the liner-less label. This makes it possible to print the liner-less label without leaving a gap between printed portions and also prevent the occurrence of a paper jam. 
     The adjustment unit  30  serves to ensure that the power required when the portable printer  101  is switched to the liner-less mode by the switching unit  10  to print the liner-less label by the thermal head  112  is greater than the power required when the portable printer  101  is switched to the standard mode by the switching unit  10  to print the backing sheet-attached label by the thermal head  112 . In general, silicon is applied on the liner-less label in an effort to increase the detachability from the adhesive surface. This often reduces the sensitivity when printing is performed by the thermal head  112 . In the present embodiment, defective printing of the liner-less label is prevented by making the power required for printing the liner-less label greater than the power required for printing the backing sheet-attached label. 
       FIG. 7  is a view illustrating a strobe signal indicative of the heating time of the thermal head within a single-dot printing period. As illustrated in  FIG. 7 , the adjustment unit  30  serves to ensure that the heating time t 2  of the thermal head  112  within the single-dot printing period T 2  (which is indicated by the strobe signal outputted to the head control unit  133 ) when the portable printer  101  is switched to the liner-less mode by the switching unit  10  is longer than the heating time t 1  of the thermal head  112  within the single-dot printing period T 1  (which is indicated by the strobe signal outputted to the head control unit  133 ) when the portable printer  101  is switched to the standard mode by the switching unit  10 . 
     In addition, the rotation speed of the platen roller  117  during the back-feed operation may be set in the same way as the discharging operation. For example, during the back-feed operation, the control unit  20  may be configure to ensure that the rotation speed of the platen roller  117  in the liner-less mode is lower than that in the standard mode. By doing so, the torque of the platen roller  117  when back-feeding the liner-less label may be set to be greater than the torque of the platen roller  117  when back-feeding the backing sheet-attached label. Further, a rotation speed of the platen roller  117  for back-feed operation used in the control processing of the rotation speed of the platen roller  117  may also be stored in the flash memory  14 . 
     In the following, the process of controlling the rotation speed of the platen roller  117  will be described with reference to  FIG. 8 , a flowchart illustrating a process to control the rotation speed of the platen roller. 
     Before the thermal head  112  starts printing, the control unit  20  determines whether the mode switched by the switching unit  10  is the standard mode or the liner-less mode (act A 801 ). 
     If the mode switched by the switching unit  10  is the standard mode (i.e., in the standard mode in act A 801 ), the control unit  20  determines the rotation speed associated with the standard mode in the rotation speed table stored in the flash memory  14  to be the rotation speed of the platen roller  117  in the standard mode (act A 802 ). On the other hand, if the mode switched by the switching unit  10  is the liner-less mode (i.e., in the liner-less mode in act A 801 ), the control unit  20  determines the rotation speed associated with the liner-less mode in the rotation speed table stored in the flash memory  14  to be the rotation speed of the platen roller  117  in the liner-less mode (act A 803 ). 
     Then, the control unit  20  determines the drive pulse period T according to the rotation speed of the platen roller  117  as determined above, and causes the motor control unit  134  to output a drive pulse signal having the determined period T to the stepping motor  131 . This allows the platen roller  117  to start discharging the backing sheet-attached label or the liner-less label from the paper roll PR (act A 804 ). 
     If the discharge of the backing sheet-attached label or the liner-less label from the paper roll PR starts, the adjustment unit  30  outputs a strobe signal to the head control unit  133  so that the thermal head  112  can start printing (act A 805 ). 
     If the print data stored in the RAM  13  are printed on the backing sheet-attached label or the liner-less label, the adjustment unit  30  stops outputting the strobe signal to the head control unit  133  so that the thermal head  112  can terminate printing (act A 806 ). 
     Subsequently, if the thermal head  112  terminates printing, the control unit  20  stops outputting the drive pulse signal to the stepping motor  131  to thereby terminate the discharge of the backing sheet-attached label or the liner-less label from the paper roll PR (act A 807 ). 
     Next, the process of controlling the back-feed of the backing sheet-attached label or the liner-less label will be described with reference to  FIG. 9 , a flowchart illustrating the processing flow to back-feed the backing sheet-attached label or the liner-less label. 
     If the thermal head  112  terminates printing, the control unit  20  determines whether the mode switched by the switching unit  10  is the standard mode or the liner-less mode (act A 901 ). 
     If the mode switched by the switching unit  10  is the standard mode (i.e., in the standard mode in act A 901 ), the control unit  20  determines the back-feed length associated with the standard mode in the back-feed length table stored in the flash memory  14  to be the back-feed length in the standard mode (act A 902 ). On the other hand, if the mode switched by the switching unit  10  is the liner-less mode (i.e., in the liner-less mode in act A 901 ), the control unit  20  determines the back-feed length associated with the liner-less mode in the back-feed length table stored in the flash memory  14  to be the back-feed length in the liner-less mode (act A 903 ). 
     Then, the control unit  20  outputs a drive pulse signal to the stepping motor  131  to start back-feeding the backing sheet-attached label or the liner-less label positioned in the paper outlet  110  (act A 904 ). While back-feeding the backing sheet-attached label or the liner-less label, the control unit  20  determines whether the back-fed length of the backing sheet-attached label or the liner-less label reaches the determined back-feed length (act A 905 ). 
     If it is determined that the back-fed length of the backing sheet-attached label or the liner-less label reaches the determined back-feed length (i.e., in case of “Yes” in act A 905 ), the control unit  20  stops outputting the drive pulse signal to the stepping motor  131  to thereby terminate the back-feeding of the backing sheet-attached label or the liner-less label (act A 906 ). 
     The operation 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) in the form of an installable or executable file. 
     In addition, the operation 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 so that the program can be downloaded from the computer via the network. Moreover, the operation program executed in the portable printer  101  of the present embodiment may be provided or distributed via a network such as the Internet. 
     In the portable printer  101  of the present embodiment described above, the operation of the stepping motor  131  is controlled according to the switching of the portable printer  101  to the standard mode or the liner-less mode. By doing so, the torque of the platen roller  117  when discharging the liner-less label from the paper roll PR can be made greater than the torque of the platen roller  117  when discharging the backing sheet-attached label from the paper roll PR. This may reduce the load applied to the stepping motor  131  when stripping the liner-less label from the paper roll PR to print the liner-less label. In particular, when the portable printer  101  of the present embodiment is operated with the electric power supplied from the rechargeable battery  270 , the load of the stepping motor  131  may be reduced. This may reduce consumption of the rechargeable battery  270  and make the operation of the portable printer  101  last for a longer period of time. In addition, it is possible to prevent the liner-less label from being bent when back-feeding the liner-less label, consequently preventing occurrence of a paper jam. Moreover, it is possible to reduce the wasting of the liner-less label by increasing the print area thereof. 
     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 a 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. 
     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 embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments 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.