Abstract:
A thermal printer includes a control part; a thermal head that is heated upon a heating instruction from the control part and stops heating upon a heating-ending instruction from the control part; a temperature detector that detects a temperature of the thermal head upon a temperature detection instruction from the control part; and a feed motor that is driven upon a conveyance instruction from the control part and stops the conveyance upon a conveyance-ending instruction from the control part. The control part issues, prior to printing, the heating instruction and the conveyance instruction such that the heating of the thermal head and the conveyance of the paper are performed in parallel. The control part issues the temperature detection instruction as an interrupt every predetermined period of time after the heating instruction is issued, and issues the heating-ending instruction when the temperature of the thermal head reaches a predetermined preheat-ending temperature.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a thermal printer having a thermal head. 
   2. Background Information 
   A thermal printer that performs printing with a thermal head is well known. In such thermal printer, prior to the start of the printing operation, it is necessary to preheat the thermal head. Furthermore, it is necessary to convey the paper to the printing position prior to the start of the printing operation. In known technologies, these preheating operation and paper conveyance operation are performed serially. For example, as shown in  FIG. 7 , a mechanical preparatory operation such as the conveyance of the paper is performed first, at the end of which the preheating operation is performed. 
   In the case shown in  FIG. 7 , since the preheating operation and the mechanical preparatory operation are performed serially, it takes a long time before the thermal printer is ready for the actual printing operation. Furthermore, where the preheating operation is performed before the mechanical preparatory operation, since the preheating operation and the mechanical preparatory operation are performed serially, the temperature of the thermal head is not checked until the mechanical preparatory operation is at least half way complete. This tends to result in overheating of the thermal head, which undesirably shortens the useful life of the thermal head. 
   In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved thermal printer that overcomes the above described problems. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure. 
   SUMMARY OF THE INVENTION 
   It is an object of the present invention to provide a thermal printer which enables a shorter processing time prior to printing while allowing to prolong the useful life of the thermal head. 
   The first aspect of the present invention provides a thermal printer adapted to perform printing on a paper. The thermal printer includes a casing; a control part; a thermal head pivotably supported to the casing and operatively connected to the control part such that the thermal head is heated upon a heating instruction from the control part and the heating is ended upon a heating-ending instruction from the control part; a temperature detector operatively connected to the control part such that the temperature detector detects a temperature of the thermal head upon a temperature detection instruction from the control part; and a feed motor adapted to convey the paper, the feed motor being operatively connected to the control part such that the feed motor is driven upon a conveyance instruction from the control part and that the conveyance is ended upon a conveyance-ending instruction from the control part. The control part is configured to issue, prior to printing, the heating instruction and the conveyance instruction such that the heating of the thermal head and the conveyance of the paper are performed in parallel. The control part is configured to issue the temperature detection instruction as an interrupt every predetermined period of time after the heating instruction is issued. The control part is configured to issue the heating-ending instruction when the temperature of the thermal head detected by the temperature detector reaches a predetermined preheat-ending temperature. 
   In this construction, the mechanical preparatory operation is initiated following the initiation of the preheating of the thermal head, and the temperature detector monitors the head temperature, thereby monitoring the timing at which the preheating is to be ended, during the execution of the mechanical preparatory operation. In other words, the preheating of the thermal head and the mechanical preparatory operation are executed in parallel. As a result, the overall processing time or the waiting time prior to the printing can be shortened as compared to a case in which the preheating of the thermal head and the mechanical preparatory operation are executed serially. Such shortening of the processing time prior to the printing makes the thermal printer easier to use for the user. 
   Furthermore, by performing the preheating of the thermal head and the mechanical preparatory operation in parallel, the preheating time can be lengthened. Since the preheating is performed while the mechanism preparatory operation is in progress, the preheating can be preformed for a longer period of time while still shortening the overall processing time. Accordingly, as compared to the case in which the preheating is performed quickly after the mechanism preparatory operation in order to shorten the time, the amount of current to be supplied can be reduced, so that the useful life of the thermal head can be extended. 
   In particular, since the head temperature is detected at each periodic interrupt made by the control part during the execution of the mechanical preparatory operation, finer temperature control can be accomplished. As a result, the preheating end timing can be obtained more precisely. Accordingly, it is possible to reduce the occurrence of excessive accumulation of heat due to the preheating end temperature being exceeded. Thus, the useful life of the thermal head can be prolonged. 
   In the thermal printer, the control part is preferably configured to issue the temperature detection instruction as an interrupt every 1-2 milliseconds. Accordingly, it is possible to perform finer temperature control as compared to the case in which the head temperature is not detected until one sheet of the image receiving paper is conveyed in the normal direction. As a result, the preheating end timing can be obtained more precisely. Accordingly, occurrence of an excessive accumulation of heat due to the preheating end temperature being exceeded can be reduced, so that the useful life of the thermal head can be prolonged. 
   The thermal printer preferably further includes a platen roller rotatably supported to the casing; and a mode motor operatively connected to the control part and the thermal head so as to, upon a switching instruction from the control part, switch between a head-up mode in which the thermal head is pivoted away from the platen roller, thereby allowing the conveyance of the paper, and a head-down mode in which the thermal head is pivoted toward the platen roller. The control part is configured to issue the switching instruction and the heating instruction, such that the heating of the thermal head is performed in parallel with the pivoting of the thermal head away from the platen roller. 
   The head-up operation, the paper feed operation and the head-down operation are mechanical operations that generally take time. In this construction, however, since the mechanical preparatory operation (including these operations) and the preheating of the thermal head are performed in parallel, the overall printing preparation time can be shortened, while the useful life of the thermal head can be lengthened. 
   In the thermal printer, the control part is preferably and ASIC. 
   A method of preheating a thermal head of a thermal printer before the thermal printer performs printing on a paper in accordance with another aspect of the present invention includes starting heating of the thermal head; starting conveyance of the paper such that the paper is conveyed while the thermal head is heated; detecting a temperature of the thermal head as an interrupt every predetermined period of time while the thermal head is heated; and ending the heating of the thermal head when the temperature of the thermal head reaches a predetermined preheating-ending temperature. 
   The method of preheating a thermal head of a thermal printer preferably further includes pivoting the thermal head away from a platen roller before the conveyance of the paper while the thermal head is heated; and pivoting the thermal head toward the platen roller after the conveyance of the paper. 
   These and other objects, feature, aspects and advantages of the present invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses a preferred embodiment of the present invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Referring now to the attached drawings which form a part of this original disclosure: 
       FIG. 1  is a block diagram used to illustrate a thermal printer constituting one embodiment of the present invention; 
       FIG. 2  is a block diagram used to illustrate a thermal printer constituting one embodiment of the present invention; 
       FIG. 3  is a schematic diagram used to illustrate a thermal printer constituting one embodiment of the present invention; 
       FIG. 4  is a schematic diagram used to illustrate the operating flow prior to printing in a thermal printer constituting one embodiment of the present invention; 
       FIG. 5  is a diagram used to illustrate the mechanical preparatory operation in a thermal printer constituting one embodiment of the present invention; 
       FIG. 6  is a schematic diagram used to illustrate a thermal printer constituting one embodiment of the present invention; and 
       FIG. 7  is a schematic diagram used to illustrate the operating flow of a thermal printer used for comparison. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Selected embodiments of the present invention will now be explained with reference to the drawings. It will be apparent to those skilled in the art from this disclosure that the following descriptions of the embodiments of the present invention are provided for illustration only and not for the purpose of limiting the invention as defined by the appended claims and their equivalents. 
   The thermal printer of the present invention makes it possible to shorten the overall processing time or waiting time prior to printing, and to lengthen the useful life of the thermal head. 
   Block diagrams of  FIGS. 1 and 2  illustrate a thermal printer in accordance with one embodiment of the present invention. In particular,  FIG. 2  illustrates the ASIC (application specific integrated circuit)  10  shown in  FIG. 1 .  FIG. 3  shows a schematic diagram that illustrates the thermal printer  1 . 
   The thermal printer is a so-called sublimation printer. As is shown in  FIG. 1 , this printer includes a casing  1 , an ASIC (application specific integrated circuit)  10 , a thermal head  20 , a thermistor  30 , an ink ribbon  40 , a motor driver  50 , a feed motor (paper feed/discharge motor)  60 , a mode motor  70 , paper sensors  91  and  92 , a tray sensor  93 , a cartridge sensor  94 , a marker sensor  95 , and a display part  184  which (for example) a liquid crystal display or the like. The thermal printer  1  also includes a platen roller  80  (see  FIG. 3 ), although this is omitted from  FIG. 1  for the sake of simplicity. 
   Furthermore, as is shown in  FIG. 2 , the ASIC  10  includes a CPU (central processing unit)  110 , a ROM (read only memory)  120 , a RAM (random access memory)  130 , a head controller  140 , a motor controller  150 , an A/D port  160 , a USB (universal serial bus) interface (hereafter referred to as “USB/IF”)  171 , a memory card controller  172 , an input part  173 , and a video output part  174 . 
   To describe the ASIC  10  in detail, as is shown in  FIG. 1 , the ASIC  10  controls the feed motor  60  and the mode motor  70  via the motor driver  50 . In this case, in the ASIC  10 , the motor controller  150  controls the motor driver  50  based on instructions from the CPU  110 . Particularly, the control of the motor driver  50  by the motor controller  150  can be accomplished independently from and in parallel with other controls by the CPU  110 , as is shown in  FIG. 2 . 
   Here, the feed motor  60  is a motor that is used for feeding/discharging or conveying of an image receiving paper  2  ( FIG. 3 ), which is used as a printing paper in this embodiment, with respect to the thermal head  20 . 
   The mode motor  70  is a motor that is used to control the orientation of the thermal head  20 . More specifically, the mode motor  70  is used to switch between a head-up mode, during which the thermal head  20  is moved away from the image receiving paper  2  and the platen roller  80  to separate the thermal head  20  from the image receiving paper  2 , and during which feeding and discharge of the paper are allowed (see the arrow indicating the head-up operation SP 1  in  FIG. 3 ); and a head-down mode, during which the thermal head  20  is caused to approach the image receiving paper  2  and the platen roller  80  so that the thermal head can be pressed against the image receiving paper  2  to perform the printing (see the arrow indicating the head-down operation SP 3  in  FIG. 3 ). 
     FIG. 3  schematically illustrates the head-up operation SP 1  and the head-down operation SP 3 , in which the thermal head  20  pivots about a direction perpendicular to the paper plane of  FIG. 3 . However, it would also be possible, for example, to perform the head-up operation SP 1  and the head-down operation SP 3  in a construction in which the thermal head  20  linearly moves toward and away from the platen roller  80 . 
   As is shown in  FIG. 3 , the thermal head  20  and the platen roller  80  are opposite each other. The thermal head  20  has a plurality of heating resistors or heating elements  21  on the side facing the platen roller  80 . In the thermal head  20 , the plurality of heating elements  21  are arranged in a line in a direction perpendicular to the paper plane of  FIG. 3 . Each of the heating elements  21  corresponds to a dot in the image to be printed. Moreover, the thermal head  20  has a driver (not shown in the figures) that provides a heat generating current. 
   The printing system of the thermal printer  1  will be described with reference to  FIG. 3 . The ink ribbon  40 , as is shown in  FIG. 3 , has a base film  40   a , and a dye ink layer  40   b  of yellow (Y), magenta (M), and cyan (C), which is laid on a base film  40   a , such that color printing can be accomplished by superimposing the printing in each of the colors. Furthermore, the image receiving paper  2  has a substrate  2   a  and a receiving layer  2   b  laid on the surface of the substrate  2   a.    
   In the sublimation thermal printer  1 , the ink ribbon  40  and the image receiving paper  2  are set between the thermal head  20  and the platen roller  80  so that the dye ink layer  40   b  and the receiving layer  2   b  contact each other with the ink ribbon  40  being on the side of the thermal head  20 . Then, the ink of the dye ink layer  40   b  is melted by the heat of the heating elements  21 , and this ink is transferred to the receiving layer  2   b  of the image receiving paper  2 , so that coloring and printing are accomplished. In this case, the transfer of the ink and the amount of ink transferred, i.e., the printing density or printing gradations, are controlled by the temperature of the abovementioned heating elements  21 . The printing density increases as this temperature of the heating elements  21  increases. 
   In such printing system, the control of the temperature of the abovementioned heating elements  21  is basically accomplished by the ASIC  10  that controls, based on the printing density data for the dots corresponding to the heating elements  21 , the time during which the power is to be supplied to each of the heating elements  21 . More specifically, as is shown in  FIG. 2 , the head controller  140  receives instructions from the CPU  110 , and controls the power transmission time to each of the heating elements  21  based on these instructions. 
   This control of the power transmission time by the head controller  140  can be performed independently from and in parallel with other controls of the CPU  110 . The head controller  140  not only controls the power transmission during the printing, but also controls the power transmission for the preheating prior to the printing. Specifically, the head controller  140  controls the heat generation at the heating elements  21  of the thermal head  20  under the control of the control part  100 . Furthermore, since the temperature control of the heating elements  21  can be accomplished by controlling the energy supply to these heating elements  21  in any form, another construction is also possible in which the printing energy is controlled by controlling the voltage applied to the heating elements  21  instead of the power transmission time. 
   Furthermore, as is shown in  FIGS. 1 and 2 , the thermistor  30  which is an example of the temperature detector detects the temperature of the thermal head  20  (hereafter also referred to as the “head temperature”) is disposed in the thermal head  20 . The signal from this thermistor  30  is sent to the CPU  110  via the A/D port  160  of the ASIC  10 , and the head temperature is detected. 
   The paper sensors  91  and  92  monitor the conveyance of the image receiving paper  2 , and the tray sensor  93  monitors the mounting of the paper tray (not shown in the figures). The cartridge sensor  94  monitors the mounting of a cartridge (not shown in the figures) in which the ink ribbon  40  is accommodated. The marker sensor  95  monitors a marker provided on the ink ribbon  40  for the purpose of positioning the ink ribbon  40 . Additionally, although it is not shown in  FIG. 1 , the signals of the respective sensors  91  through  95  are processed by the ASIC  10 . 
   Furthermore, as is shown in  FIG. 2 , the CPU  110  of the ASIC  10  can receives printing data and the like from the USB device  181  via the USB/IF  171 . The CPU  110  of the ASIC  10  can also receive printing data and the like from the memory card  182  via the memory card controller  172 . Furthermore, the CPU  110  can receive remote control signals from a remote controller  183  via the input part  173 . Moreover, the CPU  110  displays various types of information on the display part  184  via the video output part  174 . 
   The ROM  120  is accessible by the CPU  110 . Various types of processing and the like (described above and described later) are performed according to programs (not shown in the figures) stored in the ROM  120 . Furthermore, the RAM  130  is also accessible by the CPU  110 . For example, the CPU  110  reads and writes various types of printing data and the like from and into the RAM  130 . A flag  131  utilized in the monitoring of the head temperature described below is assigned to a portion of the RAM  130 , and the CPU  110  can also access this flag  131 . Furthermore, the CPU  110  also includes a counter or timer  111  as interrupt means for performing periodic interrupts that are utilized in the head temperature monitoring as described below. 
   The CPU  110 , the ROM  120  and the RAM  130  are collectively referred to as the “control part  100 .” As described above, the head controller  140  controls the heat generation in the thermal head  20  based on the instructions from the control part  100 . Furthermore, the feed motor  60  and the mode motor  70  are collectively referred to as the “mechanical element part  200 ” (see  FIG. 1 ). As described above, the mechanical element part  200  is controlled by the motor controller  150  via the motor driver  50  based on the instructions from the control part  100 . In other words, the mechanical element part  200  is controlled under the control of the control part  100 . 
     FIG. 4  shows a schematic diagram that illustrates the operational flow of the thermal printer  1  prior to the printing. The operations prior to printing include a preheating operation in which the thermal head  20  is preheated by transmitting power to the heating elements  21  of the thermal head  20  (see  FIG. 3 ), and a mechanical operation that physically sets the image receiving paper  2  (see  FIG. 3 ) and the thermal head  20  ready for printing. These tow operations are graphically illustrated in  FIG. 4 . Furthermore, the preheating initiation instruction SP 101  described below is issued by the control part  100  controlling the head controller  140 , more specifically the CPU  110  controlling the head controller  140  according to the programs stored in the ROM  120  and with reference to the RAM  130 . 
   First, in the thermal printer  1 , the control part  100  instructs the head controller  140  to initiate the preheating of the thermal head  20 . Accordingly, the power transmission to the thermal head  20  is started. As a result, the preheating of the thermal head  20  is initiated. (preheating initiation instruction SP 101 ). 
   Then, after the initiation of the preheating, the control part  100  executes the mechanical preparatory operation SP 0  to prepare the mechanical element part  200  for printing (mechanical preparatory operation execution instruction SP 102 ). Here,  FIG. 5  shows a diagram that illustrates the mechanical preparatory operation SP 0 . 
   As is shown in  FIG. 5 , the following plurality of operations are performed in a sequence as an example of the abovementioned mechanical preparatory operation SP 0  to set the image receiving paper  2  (see  FIG. 3 ) in a state that allows printing. More specifically, during the mechanical preparatory operation SP 0 , the mode motor  70  is driven by a switching instruction from the ASIC  10  so that the thermal head  20  is placed in a head-up position (head-up operation SP 1 , also shown in  FIG. 3 ). Then, the feed motor  60  is driven by conveyance instruction from the ASIC  10  so that the image receiving paper  2  ( FIG. 3 ) is supplied or fed to the printing initiation position, which is below the thermal head  20  (paper feed operation SP 2 ). When the image receiving paper  2  is set in the printing initiation position, the mode motor  70  is driven by another switching instruction from the ASIC  10  so that the thermal head  20  is placed in a head-down position (head-down operation SP 3 , also shown in  FIG. 3 ). These operations SP 1  through SP 3  are collectively referred to as the mechanical preparatory operation SP 0 . 
   In this case, since the thermal printer  1  has the motor controller  150  that controls the mechanical element port  200  based on the instructions from the control part  100 , the control part  100  can execute the mechanical preparatory operation SP 0  by, for example, successively sending instructions for initiation and execution of the head-up operation SP 1 , the paper feed operation SP 2 , and the head-down operation SP 3  to the motor controller  150 . 
   Furthermore, as shown in  FIG. 4 , the control part  100  detects the head temperature via the thermistor  30  at each periodic interrupt performed by the timer  111  (see  FIG. 2 ) while the mechanical preparatory operation SP 0  is being executed, and thereby monitors whether or not the head temperature has reached a preheating-ending temperature (head temperature monitoring instructions SP 103 ). When the preheating-ending temperature has been reached, the flag  131  (see  FIG. 2 ) is set.  FIG. 4  shows, for example, a case in which the preheating-ending temperature has been reached at the third temperature detection. In particular, in the thermal printer  1 , the periodic interrupts are set with a period such as 1 to 2 milliseconds, which is shorter than the conveyance time of one sheet of image receiving paper  2 . 
   Then, when the head temperature has reached the preheating end temperature, the control part  100  ends the preheating of the thermal head  20  (preheating ending instruction SP 104 ). More specifically, the control part  100  can ascertain whether or not the preheating-ending temperature has been reached from the state of the flag  131 , in other words, whether or not the flag  131  has been set. Where the flag  131  has been set, i.e., that the preheating-ending temperature has been reached, the control part  100  instructs the head controller  140  to end the preheating. In the case of this embodiment, the control part  100  instructs the head controller  140  to stop transmission of the power to the thermal head  20 . 
   In this manner, the mechanical preparatory operation SP 0  ends. This completes the operations prior to the printing. 
   In such a thermal printer  1 , the mechanical preparatory operation SP 0  (head-up operation SP 1 , the paper feed operation SP 2 , and the head-down operation SP 3 ) is initiated following the initiation of the preheating of the thermal head  20 , and the head temperature monitoring operation SP 103  monitors the head temperature during the execution of the mechanical preparatory operation SP 0 , and thereby monitors the end timing of the preheating. In other words, the preheating of the thermal head  20  and the mechanical preparatory operation SP 0  are performed at the same time in parallel. 
   By performing the preheating and the mechanical preparatory operation SP 0  in parallel in this manner, the overall processing time prior to the printing can be shortened as compared to a case (see  FIG. 7 ) in which the preheating of the thermal head and the mechanical preparatory operation are performed serially. From the user&#39;s viewpoint, this processing time prior to the printing is waiting time. Accordingly, by performing the preheating and the mechanical preparatory operation SP 0  in parallel, it is easier for the user to use the printer. 
   Furthermore, by performing the preheating and the mechanical preparatory operation SP 0  in parallel in this manner, the preheating time can be lengthened. Since the preheating is performed while the mechanism preparatory operation SP 0  is in progress, the preheating can be preformed for a longer period of time while still shortening the overall processing time. Accordingly, as compared to the case in which the preheating is performed quickly after the mechanism preparatory operation in order to shorten the time as shown in  FIG. 7 , the amount of current to be supplied can be reduced, so that the useful life of the thermal head  20  can be extended. 
   In particular, in the above described embodiment, the temperature detection during the head temperature monitoring operation SP 103  is performed at each periodic interrupt operation performed by the timer  111  during the mechanical preparatory operation SP 0 . Furthermore, the period between two interrupt operations can be set at a value shorter than the conveyance time of one sheet of the image receiving paper  2 . Accordingly, it is possible to perform finer temperature control as compared to the case in which the head temperature is not detected until one sheet of the image receiving paper is conveyed in the normal direction. As a result, the preheating end timing can be obtained more precisely. Accordingly, occurrence of an excessive accumulation of heat due to the preheating end temperature being exceeded can be reduced, so that the useful life of the thermal head can be prolonged. 
   Furthermore, in the above description, the mechanical preparatory operation includes the head-up operation SP 1 , the paper feed operation SP 2 , and the head-down operation SP 3 . However, various types of operations are conceivable as the mechanical preparatory operation SP 0  that is performed prior to the printing. In other words, by performing the preheating of the thermal head and the mechanical preparatory operation (which generally includes a time-consuming mechanical operation) in parallel, it is possible to shorten of the abovementioned printing preparation time and while allowing the useful life of the thermal head to be lengthened. For example, since the paper feed operation SP 2  requires a longer operating time than the head-up operation SP 1  or the head-down operation SP 3 , it would also be possible to perform only the paper feed operation SP 2  of the mechanical preparatory operation SP 0  in parallel with the preheating operation. 
   Furthermore, the color printing is described as an exampled in the above-described embodiment. However, the thermal printer  1  can also be applied to black and white printing. Furthermore, as shown in  FIG. 6 , the thermal printer  1  may also perform printing using as the recording paper a heat-sensitive paper  3  in which a substrate  3   a  and heat-sensitive layer  3   b  are laminated, instead of the ink ribbon  40  (see  FIG. 3 ) and the image receiving paper  2 . 
   As used herein, the following directional terms “forward, rearward, above, downward, vertical, horizontal, below and transverse” as well as any other similar directional terms refer to those directions of a device equipped with the present invention. Accordingly, these terms, as utilized to describe the present invention should be interpreted relative to a device equipped with the present invention. 
   The term “configured” as used herein to describe a component, section or part of a device includes hardware and/or software that is constructed and/or programmed to carry out the desired function. 
   Moreover, terms that are expressed as “means-plus function” in the claims should include any structure that can be utilized to carry out the function of that part of the present invention. 
   The terms of degree such as “substantially”, “about” and “approximately” as used herein mean a reasonable amount of deviation of the modified term such that the end result is not significantly changed. For example, these terms can be construed as including a deviation of at least ±5% of the modified term if this deviation would not negate the meaning of the word it modifies. 
   This application claims priority to Japanese Patent Application No. 2005-007439. The entire disclosure of Japanese Patent Application No. 2005-007439 is hereby incorporated herein by reference. 
   While only selected embodiments have been chosen to illustrate the present invention, it will be apparent to those skilled in the art from this disclosure that various changes and modifications can be made herein without departing from the scope of the invention as defined in the appended claims. Furthermore, the foregoing descriptions of the embodiments according to the present invention are provided for illustration only, and not for the purpose of limiting the invention as defined by the appended claims and their equivalents. Thus, the scope of the invention is not limited to the disclosed embodiments.