Patent Publication Number: US-2023150284-A1

Title: Printer device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2021-187077, filed on Nov. 17, 2021, the entire contents of which are incorporated herein by reference. 
     FIELD 
     Embodiments described herein relate generally to a printer device and methods related thereto. 
     BACKGROUND 
     A printer device that prints on the label paper discharges the label separated from release paper by a release unit. A release sensor that detects presence or absence of a printed label may be installed on the holding member that holds the discharged label (. The release sensor is composed of an inexpensive optical sensor and is installed on the outside of the housing of a label printer together with the holding member that holds the discharged label. 
     In such a printer device, since the release sensor is easily affected by external light, there is a possibility of erroneously detecting presence or absence of a label. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a diagram showing an example of a schematic structure of a label printer according to a first embodiment; 
         FIG.  2    is a diagram illustrating a structure and an operating principle of a release sensor included in the label printer; 
         FIG.  3    is a diagram showing an example of a signal output detected by the release sensor under external light; 
         FIG.  4    is a functional block diagram showing an example of a functional configuration of the label printer; 
         FIG.  5    is a flowchart showing an example of a flow of printing operation of the label printer; 
         FIG.  6    is a flowchart showing an example of a flow of a process for determining presence or absence of a label in the flowchart of  FIG.  5   ; 
         FIG.  7    is a diagram illustrating a method of setting a threshold value for determining the presence or absence of the label according to an intensity of external light; 
         FIG.  8    is a cross-sectional view showing an example of an internal structure of a label printer according to a second embodiment; 
         FIG.  9    is a diagram illustrating a structure and an operating principle of a label sensor included in the label printer; 
         FIG.  10    is a diagram showing an example of a signal output detected by the label sensor under external light; 
       and 
         FIG.  11    is a flowchart showing an example of a flow of printing operation of the label printer. 
     
    
    
     DETAILED DESCRIPTION 
     An aspect to be solved by exemplary embodiments is to provide a printer device capable of reliably detecting the presence of a printed label even if the printed label is at a position illuminated by external light. 
     In general, according to one embodiment, the printer device includes a light irradiation unit, a light irradiation control unit, a light receiving unit, and a label presence or absence determination unit. The light irradiation unit irradiates the area illuminated by the external light where a label on which printing is completed exists with light. The light irradiation control unit switches between light irradiation and non-irradiation by the light irradiation unit. The light receiving unit acquires an optical signal from the area where the label on which printing is completed exists in synchronization with the light irradiation and non-irradiation by the light irradiation control unit. The label presence or absence determination unit determines the presence or absence of a label based on a first signal acquired by the light receiving unit if the light irradiation unit is not emitting light, and a second signal acquired by the light receiving unit if the light irradiation unit is emitting light. 
     First Embodiment 
     Hereinafter, a first embodiment of a label printer according to the exemplary embodiment will be described in detail with reference to the accompanying drawings. 
     Overall Configuration of Label Printer 
     A schematic configuration of a label printer  10  according to the first embodiment will be described with reference to  FIG.  1   .  FIG.  1    is a diagram showing an example of a schematic structure of the label printer  10  according to the first embodiment. The label printer  10  is an example of the printer device in the present disclosure. 
     The label printer  10  includes a label roll  12  in which label paper  13 , which is an example of printing paper, is wound in a roll shape inside a housing  11 . Then, the label printer  10  prints while pulling out the label paper  13  from the label roll  12 . 
     The label paper  13  is wound in a roll shape with a label  14  attached to release paper  15 . The label paper  13  pulled out from the label roll  12  is conveyed toward a discharge port  21  in a state of being sandwiched between a platen roller  17  and a thermal head  16 . At this time, the label  14  which is the printing surface is located on the thermal head  16  side. The platen roller  17  is rotationally driven by a drive motor  18  such as a stepping motor. 
     The thermal head  16  has a structure in which a plurality of heating elements are arranged, and by making the heating elements corresponding to the printing pattern generate heat, printing is performed on the label  14  sandwiched between the thermal head  16  and the platen roller  17 . The label printer  10  may be a type of performing printing by sandwiching an ink ribbon (not shown) between the thermal head  16  and the label  14  and transferring the ink of the ink ribbon heated by the thermal head  16  to the label  14 . 
     The back surface side of the label  14  is an adhesive layer and the label  14  is attached to the release paper  15  by the adhesive layer. The label paper  13  on which printing is completed is separated into the label  14  and the release paper  15  at a release bar  19 . The release bar  19  is a V-shaped columnar member having two surfaces that intersect each other at an acute angle. The release bar  19  is installed along a Y axis. Before the start of printing, the release paper  15  is folded downward (on the negative side of a Z axis) at the intersection of the two surfaces of the release bar  19  and is sandwiched between the platen roller  17  and a release roller  20 . Therefore, if the platen roller  17  rotates and printing is performed on the label  14 , the release paper  15  is conveyed in the negative direction of the Z axis while being sandwiched between the platen roller  17  and the release roller  20 . Then, the label  14  attached to the release paper  15  is separated from the release paper  15  at the intersection of the two surfaces of the release bar  19 . 
     The label  14  separated from the release paper  15  is discharged from the discharge port  21  and stays at a position on the upper part of a holding member  22 . 
     Inside the holding member  22 , a release sensor  23  for detecting the presence or absence of the label  14  is installed. The release sensor  23  detects whether or not the label  14  released from the label paper  13  exists on the upper part of the holding member  22 . If the release sensor  23  detects the label  14 , the label printer  10  suspends the conveyance and printing of the label paper  13 . Then, if the user removes the label  14  on which printing is completed from the upper part of the holding member  22 , the release sensor  23  detects that the label  14  does not exist, and resumes the conveyance and printing of the label paper  13 . A structure and an operating principle of the release sensor  23  will be described later. 
     Structure and Operating Principle of Release Sensor 
     The structure and the operating principle of the release sensor  23  will be described with reference to  FIGS.  2  and  3   .  FIG.  2    is a diagram illustrating the structure and the operating principle of the release sensor  23  included in the label printer  10  according to the first embodiment.  FIG.  3    is a diagram showing an example of a signal output detected by the release sensor  23  under external light. 
     The release sensor  23  includes a light emitting element  31  and a light receiving element  34 . The light emitting element  31  emits light at a predetermined cycle by the action of a drive circuit (not shown). The light emitting element  31  is, for example, a light emitting diode (LED). Hereinafter, the light emitting element  31  is also referred to as an LED  31 . Any wavelength of the light emitted by the light emitting element  31  can be used but it is desirable to use near-infrared light which is invisible light. Further, it is desirable that the light receiving element  34  has a high sensitivity to light having the same wavelength as the light emitted by the light emitting element  31 . Therefore, a filter that transmits light having the wavelength emitted by the light emitting element  31  may be installed on the surface of the light receiving element  34 . 
     The light receiving element  34  outputs an electric signal according to the amount of received light in synchronization with a timing if the light emitting element  31  emits light. The light receiving element  34  is, for example, a photodiode. As described above, the release sensor  23  is a reflection type sensor in which the light receiving element  34  detects the reflected light of light emitted by the light emitting element  31 . 
     The light emitting element  31  emits light toward the upper side of the holding member  22  from the gap  35  of a paper conveyance mold  27  formed on the upper part of the holding member  22 . The light receiving element  34  detects the reflected light from the label  14  placed in the back of the gap  35  (on the positive side of the Z axis). It is assumed that the gap  35  is formed by cutting out a part of the paper conveyance mold  27  along the direction in which the label  14  is discharged, that is, along an X axis. 
     A detection state Sa shown in  FIG.  2    shows how the emitted light  32  emitted by the LED  31  is reflected by the label  14  and the reflected light  33  is detected by the light receiving element  34 . 
     At this time, as shown in a detection state Sb, the emitted light  32  emitted by the LED  31  passes through the gap  35  and then is reflected by the back surface (adhesive layer) of the label  14 . Then, the reflected light  33  is detected by the light receiving element  34 . 
     On the other hand, if the label  14  does not exist on the upper part of the paper conveyance mold  27 , the emitted light  32  emitted by the LED  31  passes through the gap  35 , and then, penetrates above (on the positive side of the Z axis) the paper conveyance mold  27 , as shown in a detection state Sc in  FIG.  2   . Therefore, the emitted light  32  emitted by the LED  31  is not detected by the light receiving element  34 . 
     Next, the signal output detected by the release sensor  23  under external light  38  will be described with reference to  FIG.  3   . 
     The paper conveyance mold  27  is provided at a position facing the outside of the housing  11  so that the label  14  on which printing is completed can be easily taken out. Therefore, the printed surface of the label  14  on which printing is completed is irradiated with the external light  38  in the environment in which the label printer  10  is placed. The external light  38  includes indoor lighting such as fluorescent lamps, incandescent lamps, and LED lighting, and sunlight. Such external light  38  may have an adverse effect if the release sensor  23  detects the presence or absence of the label  14 . 
     A detection state Sd shown in  FIG.  3    shows a state in which the printed surface of the label  14  is exposed to the external light  38  in a state where the label  14  is on which printing is completed on the paper conveyance mold  27 . 
     In the detection state Sd, the emitted light  32  from the LED  31  is reflected by the back surface (adhesive layer) of the label  14  to generate the reflected light  33 . Then, the light receiving element  34  detects the reflected light  33 . At this time, if the surface of the label  14  is exposed to the external light  38 , a part of the external light  38  passes through the label  14  and reaches the light receiving element  34  together with the reflected light  33  depending on an intensity of the external light  38  and a transmittance of the label  14 . Therefore, in the detection state Sd, the light receiving element  34  outputs a larger sensor output V as compared with the case where there is no external light  38 , regardless of whether the LED  31  is emitting the emitted light  32  or not. 
     The sensor output V obtained if the LED  31  illuminates the emitted light  32  is larger than the sensor output V obtained if the LED  31  does not illuminate the emitted light  32  by an amount corresponding to an intensity of the reflected light  33 . Therefore, regardless of the intensity of the external light  38 , the release sensor  23  can determine that the label  14  is present if a difference value between the sensor output V obtained if the LED  31  emits the emitted light  32  and the sensor output V obtained if the LED  31  does not emit the emitted light  32  is equal to or greater than a preset threshold value. 
     A detection state Se shown in  FIG.  3    shows a state in which the surface of the paper conveyance mold  27  is exposed to the external light  38  without the label  14 . 
     In the detection state Se, the emitted light  32  from the LED  31  passes through the gap  35  (see  FIG.  2   ) of the paper conveyance mold  27  and is radiated into the space. Therefore, the reflected light generated by the emitted light  32  is not detected by the light receiving element  34 . At this time, if the surface of the paper conveyance mold  27  is exposed to the external light  38 , the external light  38  passes through the gap  35  and reaches the light receiving element  34 , and thus the light receiving element  34  outputs the sensor output V corresponding to the intensity of the external light  38 . And this state is not related to the emission state of the emitted light  32  by the LED  31 . Therefore, in the detection state Se, there is almost no difference between the sensor output V obtained if the LED  31  emits the emitted light  32  and the sensor output V obtained if the LED  31  does not emit the emitted light  32 . Therefore, regardless of the intensity of the external light  38 , the release sensor  23  can determine that the label  14  does not exist if the difference value between the sensor output V obtained if the LED  31  emits the emitted light  32  and the sensor output V obtained if the LED  31  does not emit the emitted light  32  is less than the preset threshold value. 
     Hereinafter, a method of determining the presence or absence of the label  14  based on a waveform of the actual sensor output V will be described. The sensor output example Ca shown in  FIG.  3    shows an example of the sensor output V if the label  14  is on the paper conveyance mold  27  and there is no external light  38 . 
     The LED  31  repeatedly switches between a lighting state and an extinguishing state at a predetermined timing. In a case of the sensor output example Ca, the LED  31  is turned on between time ta and time tb, and between time tc and time td. On the other hand, the LED  31  is turned off before the time ta, between the time tb and the time tc, and after the time td. The period in which the LED  31  is turned on is defined as a lighting period pa, and the period in which the LED  31  is turned off is defined as an extinguishing period pb. The lengths of the lighting period pa and the extinguishing period pb are freely set. Further, the ratio (duty ratio) of the lighting period pa and the extinguishing period pb can be set to any ratio. 
     At this time, the sensor output V output by the light receiving element  34  exhibits a pulse waveform as shown in the sensor output example Ca. That is, a very small sensor output V can be obtained during the extinguishing period pb of the LED  31 . Then, in the lighting period pa, the sensor output V corresponding to the emitted light  32  of the LED  31  is obtained. Then, a difference value ΔV is generated between the sensor output V in the lighting period pa and the sensor output V in the extinguishing period pb. 
     Here, it is assumed that the sensor output V is generated by positive logic, that is, the larger the amount of light received by the light receiving element  34 , the larger the sensor output V is output. The sensor output V may be generated by negative logic. That is, the smaller sensor output V may be output as the amount of light received by the light receiving element  34  increases. 
     On the other hand, the sensor output example Cb shown in  FIG.  3    shows an example of the sensor output V if there is no label  14  on the paper conveyance mold  27  and there is no external light  38 . Lighting and extinguishing timings of the LED  31  in the sensor output example Cb are the same as those described in the sensor output example Ca. 
     At this time, the sensor output V output by the light receiving element  34  is substantially equal regardless of whether the LED  31  is turned on or off, as shown in the sensor output example Cb. That is, the difference value ΔV between the sensor output V in the lighting period pa and the sensor output V in the extinguishing period pb is a very small value. 
     From the comparison between the sensor output example Ca and the sensor output example Cb, if there is no external light  38 , the difference value ΔV between the sensor output V in the lighting period pa and the sensor output V in the extinguishing period pb is compared with the threshold value. If the difference value ΔV is equal to or greater than the threshold value, it can be determined that the label  14  exists. Further, if the difference value ΔV is less than the threshold value, it can be determined that the label  14  does not exist. 
     The sensor output example Cc shown in  FIG.  3    shows an example of the sensor output V if the label  14  is on the paper conveyance mold  27  and the external light  38  is present. Lighting and extinguishing timings of the LED  31  in the sensor output example Cc are the same as those described in the sensor output example Ca. 
     At this time, the sensor output V output by the light receiving element  34  exhibits a pulse waveform as shown in the sensor output example Cc. That is, a small sensor output V can be obtained during the extinguishing period pb of the LED  31 . The sensor output V obtained during the extinguishing period pb of the LED  31  has a larger value than the sensor output V obtained at the same timing of the sensor output example Ca by the amount that the external light  38  passed through the label  14  reaches the light receiving element  34 . Then, in the lighting period pa, a sensor output V larger than that in the extinguishing period pb can be obtained. Then, the difference value ΔV is generated between the sensor output V in the lighting period pa and the sensor output V in the extinguishing period pb. 
     On the other hand, the sensor output example Cd shown in  FIG.  3    shows an example of the sensor output V if there is no label  14  on the paper conveyance mold  27  and there is external light  38 . The lighting and extinguishing timings of the LED  31  in the sensor output example Cd are the same as those described in the sensor output example Ca. 
     At this time, the sensor output V output by the light receiving element  34  has substantially the same value corresponding to the intensity of the external light  38  regardless of whether the LED  31  is turned on or off, as shown in the sensor output example Cd. That is, the difference value ΔV between the sensor output V in the lighting period pa and the sensor output V in the extinguishing period pb is a very small value. 
     From the comparison between the sensor output example Cc and the sensor output example Cd, if the external light  38  is present, the difference value ΔV between the sensor output V in the lighting period pa and the sensor output V in the extinguishing period pb is compared with the threshold value. If the difference value ΔV is equal to or greater than the threshold value, it can be determined that the label  14  exists. Further, if the difference value ΔV is less than the threshold value, it can be determined that the label  14  does not exist. 
     That is, regardless of the presence or absence of the external light  38 , if the difference value ΔV between the sensor output V in the lighting period pa and the sensor output V in the extinguishing period pb is compared with the threshold value. If the difference value ΔV is equal to or greater than the threshold value, it can be determined that the label  14  exists. Further, if the difference value ΔV is less than the threshold value, it can be determined that the label  14  does not exist. 
     Functional Configuration of Label Printer 
     A functional configuration of the label printer  10  will be described with reference to  FIG.  4   .  FIG.  4    is a functional block diagram showing an example of the functional configuration of the label printer  10 . 
     The control unit (not shown) included in the label printer  10  has a computer configuration and operates by executing a control program stored in the control unit. The control unit implements a light irradiation unit  41 , a light irradiation control unit  42 , a light receiving unit  43 , a label presence or absence determination unit  44 , and a print control unit  45  shown in  FIG.  4    as functional units. 
     The light irradiation unit  41  irradiates the area illuminated by the external light  38  where the label  14  on which printing is completed exists with light from the light emitting element  31 . 
     The light irradiation control unit  42  switches between light irradiation and non-irradiation by the light irradiation unit  41 . 
     The light receiving unit  43  acquires an optical signal from the area where the label  14  on which printing is completed exists in synchronization with the light irradiation and non-irradiation by the light irradiation control unit  42 , by the light receiving element  34 . 
     The label presence or absence determination unit  44  determines the presence or absence of the label  14  based on the sensor output V (first signal) acquired by the light receiving unit  43  if the light irradiation unit  41  is not emitting light and the sensor output V (second signal) acquired by the light receiving unit  43  if the light irradiation unit  41  is emitting light. 
     The print control unit  45  acquires print content and an instruction to start printing and instructs each unit of the label printer  10  to start printing. Further, the print control unit  45  suspends printing of a next label on a condition that the label presence or absence determination unit  44  determines that the label  14  is present. Further, the print control unit  45  instructs each unit of the label printer  10  to start printing of a next label on a condition that the label presence or absence determination unit  44  determines that there is no label  14 . Further, the print control unit  45  determines whether or not a predetermined number of sheets of labels  14  are printed. 
     Flow of Printing Operation Performed by Label Printer 
     A flow of a printing process performed by the label printer  10  will be described with reference to  FIGS.  5  and  6   .  FIG.  5    is a flowchart showing an example of a flow of printing operation of the label printer  10  according to the first embodiment.  FIG.  6    is a flowchart showing an example of a flow of a process for determining the presence or absence of the label  14  in the flowchart of  FIG.  5   . 
     The print control unit  45  instructs each unit of the label printer  10  to start printing (ACT  11 ). 
     The label presence or absence determination unit  44  performs a label presence or absence determination process for determining the presence or absence of the label  14  (ACT  12 ). If it is determined that the label  14  is present, the process proceeds to ACT  13 . On the other hand, if it is not determined that the label  14  is present, the process proceeds to ACT  14 . A detailed flow of the label presence or absence determination process will be described later (see  FIG.  6   ). 
     If it is determined in ACT  12  that the label  14  is present, the print control unit  45  suspends the printing operation (ACT  13 ). After that, the process returns to ACT  12 , and the label presence or absence determination process is repeated. 
     In ACT  12 , if it is determined that there is no label  14 , that is, it is determined that the label  14  on which printing is completed is removed from the holding member  22 , the print control unit  45  determines whether printing is performed on the predetermined number of sheets of labels  14  (ACT  14 ). If it is determined that printing is performed on the predetermined number of sheets of labels  14  (ACT  14 : Yes), the label printer  10  ends the process of  FIG.  5   . On the other hand, if it is not determined that printing is performed on the predetermined number of sheets of labels  14  (ACT  14 : No), the process proceeds to ACT  15 . 
     If it is not determined in ACT  14  that printing is performed on the predetermined number of sheets of labels  14 , the print control unit  45  resumes printing (ACT  15 ). 
     The print control unit  45  increments the number of labels  14  on which printing is completed (ACT  16 ). Then, the process returns to ACT  12 . 
     Next, the flow of the label presence or absence determination process will be described with reference to  FIG.  6   . 
     First, the light irradiation control unit  42  turns off the LED  31  with respect to the light irradiation unit  41  (ACT  21 ). 
     The light receiving unit  43  detects the sensor output V (first signal) of the light receiving element  34  (ACT  22 ). 
     The light irradiation control unit  42  turns on the LED  31  with respect to the light irradiation unit  41  (ACT  23 ). 
     The light receiving unit  43  detects the sensor output V (second signal) of the light receiving element  34  (ACT  24 ). 
     The label presence or absence determination unit  44  calculates the difference value ΔV between the second signal and the first signal (ACT  25 ). 
     The label presence or absence determination unit  44  determines whether the difference value ΔV is equal to or greater than the threshold value Th (ACT  26 ). If it is determined that the difference value ΔV is equal to or greater than the threshold value Th (ACT  26 : Yes), the process proceeds to ACT  27 . On the other hand, if it is not determined that the difference value ΔV is equal to or greater than the threshold value Th (ACT  26 : No), the process proceeds to ACT  28 . 
     If it is determined in ACT  26  that the difference value ΔV is equal to or greater than the threshold value Th, the label presence or absence determination unit  44  determines that the label  14  is on the holding member  22  (paper conveyance mold  27 ) (ACT  27 ). After that, the process returns to the main routine ( FIG.  5   ). 
     If it is determined in ACT  26  that the difference value ΔV is less than the threshold value Th, the label presence or absence determination unit  44  determines that there is no label  14  on the holding member  22  (paper conveyance mold  27 ) (ACT  28 ). After that, the process returns to the main routine ( FIG.  5   ). 
     Method of Setting Threshold Value 
     A method of setting the threshold value Th for determining the presence or absence of the label  14  will be described with reference to  FIG.  7   .  FIG.  7    is a diagram illustrating the method of setting the threshold value Th for determining the presence or absence of the label  14 , depending on the intensity of external light. 
     As shown in the sensor output example Ce of  FIG.  7   , the sensor output V has a form in which a pulse-shaped output corresponding to if the LED  31  is turned on is superimposed on the sensor output V corresponding to if the LED  31  is turned off. This form is maintained even if the external light  38  becomes stronger, but as the external light  38  becomes stronger, the sensor output V increases, and as shown in the sensor output example Cf of  FIG.  7   , the sensor output corresponding to if the LED  31  is turned off increases from a sensor output Va to a sensor output Vb. Further, since the emitted light  32  if the LED  31  is turned on is constant, the stronger the external light  38 , the smaller the ratio of the emitted light  32  to the intensity of the external light  38 . Therefore, the stronger the external light  38 , the smaller the difference value ΔV of the sensor outputs V. 
     That is, in the example shown in  FIG.  7   , a difference value ΔVb if the external light  38  is strong is smaller than a difference value ΔVa if the external light  38  is weak. 
     Therefore, in an environment where the intensity of the external light  38  changes, it is difficult to determine the presence or absence of the label  14  by comparing the difference value ΔV with the fixed threshold value Th. Therefore, it is desirable that the label printer  10  has a function of setting the threshold value Th according to the intensity of the external light  38 . 
     As described above, the sensor output V corresponding to if the LED  31  is turned off increases as the external light  38  becomes stronger. Then, the difference value ΔV decreases as the external light  38  becomes stronger. Therefore, it is desirable that the label presence or absence determination unit  44  sets a threshold value Th (V) that decreases monotonically according to the sensor output V if the LED  31  is turned off. More specifically, it is desirable that the label presence or absence determination unit  44  has a threshold value setting table T shown in  FIG.  7    and sets the threshold value Th (V) that decreases monotonically as the external light  38  increases. In  FIG.  7   , the threshold value Th (V) is linearly decreased with the increase of the sensor output V if the LED  31  is turned off, but the exemplary embodiment is not limited thereto. For example, the threshold value Th (V) may be decreased non-linearly with the increase of the sensor output V if the LED  31  is turned off. The threshold value Th (V) is determined using the results of evaluation experiments conducted in advance. 
     Although not shown, flicker may occur in which the brightness of the illumination fluctuates periodically depending on the illumination conditions of the environment in which the label printer  10  is placed. If flicker occurs, the fluctuation of the illumination light due to the flicker is superimposed on the sensor output V. Therefore, depending on a timing of acquiring the sensor output V if the LED  31  is turned off and the sensor output V if the LED  31  is turned on, a difference value ΔV different from the actual one may be calculated. 
     In order to reduce the influence of such flicker, the label presence or absence determination unit  44  may calculate an average value of the sensor output V in the section for each of the extinguishing period pb of the LED  31  and the lighting period pa of the LED  31  and may calculate the difference value ΔV from the calculated average value of the sensor output V if the LED  31  is turned off and the calculated average value of the sensor output V if the LED  31  is turned on. In addition to the average value, the maximum value within the period may be calculated, or the minimum value within the period may be calculated. 
     Action and Effect of Embodiment 
     As described above, the label printer  10  of the first embodiment includes the light irradiation unit  41  that irradiates the area illuminated by the external light  38  where the label  14  on which printing is completed exists with light, the light irradiation control unit  42  that switches between the light irradiation and non-irradiation by the light irradiation unit  41 , the light receiving unit  43  that acquires the optical signal from the area where the label  14  on which printing is completed exists in synchronization with the light irradiation and non-irradiation by the light irradiation control unit  42 , and the label presence or absence determination unit  44  that determines the presence or absence of the label  14  based on the first signal acquired by the light receiving unit  43  if the light irradiating unit  41  is not emitting light, and the second signal acquired by the light receiving unit  43  if the light irradiating unit  41  is emitting light. Therefore, even if the printed label  14  is at a position illuminated by the external light  38 , the presence of the printed label  14  can be reliably detected. 
     Further, in the label printer  10  of the first embodiment, the light irradiation unit  41  and the light receiving unit  43  are installed on the same side of the label surface of the label  14  on which printing is completed. Therefore, the light irradiation unit  41  and the light receiving unit  43  can be installed in a small space. 
     Further, in the label printer  10  of the first embodiment, the label presence or absence determination unit  44  determines the presence or absence of the label  14  on which the printing is completed, based on the magnitude relationship between the difference value ΔV between the level of the first signal and the level of the second signal and the threshold value Th. Therefore, the presence or absence of the label  14  can be detected by simple signal processing. 
     Further, in the label printer  10  of the first embodiment, the label presence or absence determination unit  44  sets the threshold value Th (V) based on the level of the first signal (sensor output V). Therefore, even if the intensity of the external light  38  changes, the presence or absence of the label  14  can be reliably detected. 
     Further, the label printer  10  of the first embodiment further includes the print control unit  45  that suspends the printing of the next label  14  on the condition that the label presence or absence determination unit  44  determines that the label  14  is present, and resumes printing of the next label  14  on the condition that the label presence or absence determination unit  44  determines that there is no label  14 . Therefore, it is possible to prevent the printed label  14  from staying in the discharge port  21 . 
     Second Embodiment 
     Hereinafter, a second embodiment of the label printer according to the exemplary embodiment will be described in detail with reference to the accompanying drawings. 
     Overall Configuration of Label Printer 
     A schematic configuration of a label printer  40  according to the second embodiment will be described with reference to  FIG.  8   .  FIG.  8    is a cross-sectional view showing an example of an internal structure of the label printer  40  according to the second embodiment. The label printer  40  is an example of the printer device in the present disclosure. 
     The label printer  40  includes the label roll  12  in which linerless label paper  26 , which is an example of printing paper, is wound in a roll shape inside the housing  11 . Then, the label printer  40  prints while pulling out the linerless label paper  26  from the label roll  12 . 
     The linerless label paper  26  has a printed surface on the front surface and an adhesive surface on the back surface. That is, the linerless label paper  26  is a label paper without the release paper  15  (see  FIG.  1   ). The linerless label paper  26  pulled out from the label roll  12  is conveyed toward the discharge port  36  in a state of being sandwiched between the platen roller  17  and the thermal head  16 . At this time, the printing surface of the linerless label paper  26  is located on the thermal head  16  side. The linerless label paper  26  is an example of the label in the present disclosure. 
     The thermal head  16  prints on the printing surface of the linerless label paper  26  sandwiched between the thermal head  16  and the platen roller  17 . The label printer  40  may be a type of performing printing by sandwiching an ink ribbon (not shown) between the thermal head  16  and the linerless label paper  26  and transferring the ink of the ink ribbon heated by the thermal head  16  on the printing surface of the linerless label paper  26 . 
     The linerless label paper  26  discharged from the discharge port  36  stays at the position on the upper part of the holding member  22 . Then, the linerless label paper  26  is removed from the upper part of the holding member  22  cut by a cutter  28  provided on the upstream side of the holding member  22 . The cutter  28  is composed of a fixed blade  29  provided on the back surface side of the linerless label paper  26  and a movable blade  30  provided on the printing surface side of the linerless label paper  26 , and may perform cutting by an operator&#39;s manual operation or automatically at the end of printing. 
     At the position of the holding member  22 , the label sensor  24  for detecting the presence or absence of the linerless label paper  26  (label) is installed. The label sensor  24  is installed on the upper part of the holding member  22  at a position facing each other across the label surface of the linerless label paper  26 , and detects whether or not the linerless label paper  26  exists. If the label sensor  24  detects the linerless label paper  26 , the label printer  40  suspends the conveyance and printing of the linerless label paper  26 . Then, if the user removes the linerless label paper  26  on which printing is completed, the label sensor  24  detects that the linerless label paper  26  does not exist, and resumes the conveyance and printing of the linerless label paper  26 . A structure and an operating principle of the label sensor  24  will be described later. 
     Further, since a functional configuration of the label printer  40  is the same as the functional configuration of the label printer  10  described above (see  FIG.  4   ), the description thereof will be omitted. Further, in the following description, the same reference numerals as those used in  FIG.  4    are used for the description of each functional part of the label printer  40 . 
     Structure and Operating Principle of Label Sensor 
     A structure and an operating principle of the label sensor  24  will be described with reference to  FIGS.  9  and  10   .  FIG.  9    is a diagram illustrating the structure and operating principle of the label sensor  24  included in the label printer  40  according to the second embodiment.  FIG.  10    is a diagram showing an example of a signal output detected by the label sensor  24  under external light. 
     The label sensor  24  includes the light emitting element  31  and the light receiving element  34 . The light emitting element  31  emits light at a predetermined cycle by the action of a drive circuit (not shown). The light emitting element  31  is, for example, an LED. Any wavelength of the light emitted by the light emitting element  31  can be used, but it is desirable to use near-infrared light which is invisible light. Further, it is desirable that the light receiving element  34  has a high sensitivity to light having the same wavelength as the light emitted by the light emitting element  31 . Therefore, a filter that transmits light having the wavelength emitted by the light emitting element  31  may be installed on the surface of the light receiving element  34 . 
     The light receiving element  34  outputs an electric signal according to the amount of received light in synchronization with a timing if the light emitting element  31  emits light. The light receiving element  34  is, for example, a photodiode. As described above, the label sensor  24  is a transmission type sensor that detects the transmitted light of the light emitted by the light emitting element  31  by the light receiving element  34 . 
     The light emitting element  31  and the light receiving element  34  are installed at positions facing each other with the paper conveyance mold  27 , which is formed on the upper part of the holding member  22 , interposed therebetween. The light emitting element  31  emits light toward the upper side of the holding member  22  from the gap  35  of the paper conveyance mold  27  formed on the upper part of the holding member  22 . The light receiving element  34  detects the light transmitted through the gap  35 . It is assumed that the gap  35  is formed by cutting out a part of the paper conveyance mold  27  along the direction in which the linerless label paper  26  is discharged, that is, along the X axis. 
     A detection state Sf shown in  FIG.  9    shows a state in which the emitted light  32  emitted by the LED  31  is blocked by the linerless label paper  26  and the emitted light  32  is not detected by the light receiving element  34 . 
     At this time, as shown in a detection state Sg, the emitted light  32  emitted by the LED  31  passes through the gap  35  and then hits the adhesive surface of the linerless label paper  26 . Then, a small part of the emitted light  32  passes through the linerless label paper  26  and reaches the light receiving element  34 , but since the amount of the emitted light  32  transmitted through the linerless label paper  26  is small, the light receiving element  34  outputs a slightly larger sensor output V as compared with the case where there is no emitted light  32 . 
     On the other hand, if the linerless label paper  26  does not exist on the upper part of the paper conveyance mold  27 , as shown in the detection state Sh in  FIG.  9   , the emitted light  32  emitted by the LED  31  passes through the gap  35  and then penetrates above (on the positive side of the Z axis) the paper conveyance mold  27 . Then, the light receiving element  34  detects the emitted light  32  of the LED  31 . Therefore, the light receiving element  34  outputs a larger sensor output V as compared with the case where there is no emitted light  32 . 
     Next, the signal output detected by the label sensor  24  under the external light  38  will be described with reference to  FIG.  10   . 
     The paper conveyance mold  27  is located on the surface of the housing  11  so that the linerless label paper  26  on which printing is completed can be easily taken out. Then, the printed surface of the linerless label paper  26  on which printing is completed is irradiated with the external light  38  through the gap between the paper conveyance mold  27  and the installation position of the light receiving element  34  in the environment in which the label printer  40  is placed. The external light  38  includes indoor lighting such as fluorescent lamps, incandescent lamps, and LED lighting, and sunlight. Such external light  38  may have an adverse effect if the label sensor  24  detects the presence or absence of the linerless label paper  26 . 
     A detection state Si shown in  FIG.  10    shows a state in which the printing surface of the linerless label paper  26  is exposed to the external light  38  in a state where the printed linerless label paper  26  is on the paper conveyance mold  27 . 
     In the detection state Si, the emitted light  32  from the LED  31  hits the back surface (adhesive surface) of the linerless label paper  26 . Then, a part of the emitted light  32  passes through the linerless label paper  26  and reaches the light receiving element  34 , but the sensor output V output by the light receiving element  34  is very small. At this time, if the surface of the linerless label paper  26  is exposed to the external light  38 , a part of the external light  38  is reflected on the surface of the linerless label paper  26  and reaches the light receiving element  34 . Therefore, in the detection state Si, the light receiving element  34  outputs a larger sensor output V as compared with the case where there is no external light  38 , regardless of whether the LED  31  is illuminating the emitted light  32  or not. And, as described above, the sensor output V by the emitted light  32  from the LED  31  is very small. Therefore, the label sensor  24  can determine that the linerless label paper  26  is present if the difference value between the sensor output V obtained if the LED  31  emits the emitted light  32  and the sensor output V obtained if the LED  31  does not emit the emitted light  32  is less than a preset threshold value. 
     On the other hand, a detection state Sj shown in  FIG.  10    shows a state in which the surface of the paper conveyance mold  27  is exposed to the external light  38  without the linerless label paper  26 . 
     In the detection state Sj, the emitted light  32  from the LED  31  passes through the gap  35  (see  FIG.  9   ) of the paper conveyance mold  27  and reaches the light receiving element  34 . Therefore, the emitted light  32  is detected by the light receiving element  34 . At this time, a part of the external light  38  to which the surface of the paper conveyance mold  27  is exposed also reaches the light receiving element  34 . Therefore, the light receiving element  34  outputs the sensor output V, which is the sum of the emitted light  32  from the LED  31  and the reflected light of the external light  38 . 
     Further, the sensor output V obtained if the LED  31  emits the emitted light  32  is larger than the sensor output V obtained if the LED  31  does not emit the emitted light  32 . Therefore, regardless of the intensity of the external light  38 , the label sensor  24  can determine that there is no linerless label paper  26  if the difference value between the sensor output V obtained if the LED  31  emits the emitted light  32  and the sensor output V obtained if the LED  31  does not emit the emitted light  32  is equal to or greater than a preset threshold value. 
     Hereinafter, a method of determining the presence or absence of the linerless label paper  26  based on the waveform of the actual sensor output V will be described. The sensor output example Cg shown in  FIG.  10    shows an example of the sensor output V if the linerless label paper  26  is on the paper conveyance mold  27  and there is no external light  38 . 
     In any of the states shown in  FIG.  10   , the LED  31  repeatedly switches between a lighting state and an extinguishing state at the same timing as described in  FIG.  3   . 
     At this time, the sensor output V output by the light receiving element  34  exhibits a pulse waveform as shown in the sensor output example Cg. That is, a very small sensor output V can be obtained during the extinguishing period pb of the LED  31 . Then, in the lighting period pa, a part of the emitted light  32  of the LED  31  passes through the linerless label paper  26 , and thus a sensor output V slightly larger than the extinguishing period pb of the LED  31  can be obtained. Then, a very small difference value ΔV is generated between the sensor output V in the lighting period pa and the sensor output V in the extinguishing period pb. 
     On the other hand, the sensor output example Ch shown in  FIG.  10    shows an example of the sensor output V if there is no linerless label paper  26  on the paper conveyance mold  27  and there is no external light  38 . Lighting and extinguishing timings of the LED  31  in the sensor output example Ch are the same as those described in the sensor output example Ca (see  FIG.  3   ). 
     At this time, as shown in the sensor output example Ch, the light receiving element  34  generates a sensor output V corresponding to the emitted light  32  of the LED  31  during the lighting period pa of the LED  31 . Then, a difference value ΔV is generated between the sensor output V in the lighting period pa and the sensor output V in the extinguishing period pb. The difference value ΔV generated at this time is larger than the difference value ΔV generated in the sensor output example Cg because the emitted light  32  of the LED  31  is directly incident on the light receiving element  34 . 
     From the comparison between the sensor output example Cg and the sensor output example Ch, if there is no external light  38 , the difference value ΔV between the sensor output V in the lighting period pa and the sensor output V in the extinguishing period pb is compared with the threshold value. If the difference value ΔV is equal to or greater than the threshold value, it can be determined that the linerless label paper  26  does not exist. Further, if the difference value ΔV is less than the threshold value, it can be determined that the linerless label paper  26  exists. 
     The sensor output example Ci shown in  FIG.  10    shows an example of the sensor output V if the linerless label paper  26  is on the paper conveyance mold  27  and the external light  38  is present. Lighting and extinguishing timings of the LED  31  in the sensor output example Ci are the same as those described in the sensor output example Ca. 
     At this time, the sensor output V output by the light receiving element  34  exhibits a pulse waveform as shown in the sensor output example Ci. That is, during the extinguishing period pb of the LED  31 , the sensor output V becomes substantially the same value corresponding to the intensity of the reflected light on the linerless label paper  26  of the external light  38 . Then, during the lighting period pa of the LED  31 , a part of the emitted light  32  of the LED  31  passes through the linerless label paper  26  and reaches the light receiving element  34 , and thus the sensor output V slightly larger than that in the extinguishing period pb of the LED  31  is obtained. Then, a slight difference value ΔV is generated between the sensor output V in the lighting period pa and the sensor output V in the extinguishing period pb. 
     On the other hand, the sensor output example Cj shown in  FIG.  10    shows an example of the sensor output V if there is no linerless label paper  26  on the paper conveyance mold  27  and the external light  38  is present. Lighting and extinguishing timings of the LED  31  in the sensor output example Cj are the same as those described in the sensor output example Ca. 
     At this time, the sensor output V output by the light receiving element  34  exhibits a pulse waveform as shown in the sensor output example Cj. That is, during the extinguishing period pb of the LED  31 , the sensor output V corresponding to the intensity of the reflected light in the paper conveyance mold  27  of the external light  38  is obtained. If the paper conveyance mold  27  is a dark color with low reflectance, the sensor output V is smaller than the sensor output V in the extinguishing period pb of the LED  31  in the sensor output example Ci. Further, the sensor output V obtained during the lighting period pa of the LED  31  becomes a larger value than the sensor output V obtained during the extinguishing period pb of the LED  31  by the amount that the emitted light  32  of the LED  31  passed through the paper conveyance mold  27  reaches the light receiving element  34 . Then, a difference value ΔV larger than the difference value ΔV generated in the sensor output example Ci is generated between the sensor output V in the lighting period pa and the sensor output V in the extinguishing period pb. 
     From the comparison between the sensor output example Ci and the sensor output example Cj, if the external light  38  is present, the difference value ΔV between the sensor output V in the lighting period pa and the sensor output V in the extinguishing period pb is compared with the threshold value. If the difference value ΔV is equal to or greater than the threshold value, it can be determined that the linerless label paper  26  does not exist. Further, if the difference value ΔV is less than the threshold value, it can be determined that the linerless label paper  26  exists. 
     That is, regardless of the presence or absence of the external light  38 , if the difference value ΔV between the sensor output V in the lighting period pa and the sensor output V in the extinguishing period pb is compared with the threshold value. If the difference value ΔV is equal to or greater than the threshold value, it can be determined that the linerless label paper  26  does not exist. Further, if the difference value ΔV is less than the threshold value, it can be determined that the linerless label paper  26  exists. 
     Flow of Printing Operation Performed by Label Printer 
     A flow of the printing process performed by the label printer  40  will be described with reference to  FIG.  11   . FIG. 
       11  is a flowchart showing an example of the flow of the printing operation of the label printer  40  according to the second embodiment. 
     The print control unit  45  instructs each unit of the label printer  40  to start printing (ACT  31 ). 
     The label presence or absence determination unit  44  performs a label presence or absence determination process for determining the presence or absence of the linerless label paper  26  (ACT  32 ). If it is determined that the linerless label paper  26  is present, the process proceeds to ACT  33 . On the other hand, if it is not determined that the linerless label paper  26  is present, the process proceeds to ACT  35 . A detailed flow of the label presence or absence determination process is the same as the above-mentioned process flow (see  FIG.  6   ). However, only the magnitude relationship between the difference value ΔV of the sensor outputs V and the threshold value Th is different from the first embodiment. That is, in the present embodiment, if the difference value ΔV is equal to or greater than the threshold value Th, it is determined that there is no linerless label paper  26 . Further, if the difference value ΔV is less than the threshold value Th, it is determined that the linerless label paper  26  is present. 
     If it is determined in ACT  32  that the linerless label paper  26  is present, the print control unit  45  suspends the printing operation (ACT  33 ). 
     Subsequently, the print control unit  45  cuts the linerless label paper  26  by the cutter  28  (ACT  34 ). Then, the process returns to ACT  32 . The linerless label paper  26  may be cut by the user himself or herself by operating the cutter  28 . 
     In ACT  32 , if it is determined that there is no linerless label paper  26 , that is, it is determined that the linerless label paper  26  on which printing is completed is removed from the holding member  22 , the print control unit  45  determines whether or not printing is performed on a predetermined number of linerless label paper  26  (ACT  35 ). If it is determined that printing is performed on a predetermined number of sheets of linerless label paper  26  (ACT  35 : Yes), the label printer  40  ends the process of  FIG.  11   . On the other hand, if it is not determined that a predetermined number of sheets of the linerless label paper  26  are printed (ACT  35 : No), the process proceeds to ACT  36 . 
     If it is not determined in ACT  35  that printing is performed on a predetermined number of sheets of the linerless label paper  26 , the print control unit  45  resumes printing (ACT  36 ). 
     The print control unit  45  increments the number of sheets of the linerless label paper  26  on which printing is completed (ACT  37 ). Then, the process returns to ACT  32 . 
     Action and Effect of Embodiment 
     As described above, in the label printer  40  of the second embodiment, the light irradiation unit  41  and the light receiving unit  43  are installed at positions facing each other across the label surface of the linerless label paper  26  on which printing is completed. Therefore, as compared with the case of using the reflection type sensor, the amount of the external light  38  incident on the light receiving element  34  is reduced, and thus the influence of the external light  38  can be reduced. 
     In the first embodiment, it is described that the release sensor  23  is configured by using a reflection type sensor. Further, in the second embodiment, it is described that the label sensor  24  is configured by using a transmission type sensor. However, the release sensor  23  may be composed of a transmission type sensor, or the label sensor  24  may be composed of a reflection type sensor. 
     While certain embodiments have been described, 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.