Thermal printing system having function for preventing over heating of thermal head

An information printing apparatus that applies predetermined print energy to a printhead to print data received from an external data source, includes a receiver for receiving printing data from the external data source, a detector for detecting a current temperature of the printhead which is used to print information associated with the received printing data and memory for storing the received printing data. A controller controls the information printing apparatus such that when the current temperature of the printhead is below a predetermined threshold temperature the printing data received from the external data source is directly printed without storing the received printing data in memory and when the current temperature of the printhead exceeds the predetermined threshold temperature the print head is prevented from printing out the printing data and the received printing data is stored in the memory means until the current temperature is below the predetermined threshold temperature at which time the stored data is printed.

BACKGROUND OF THE INVENTION 
The present invention relates to a thermal printing system (or thermal 
printer) using a thermal head for changing, according to input printing 
data, a color of proper parts of a recording sheet by causing the thermal 
head to come in contact with the recording sheet appropriately so as to 
print an image corresponding to the input printing data on the recording 
sheet. Such a recording sheet comprises a paper which is normally 
specially coated so that the special coating discolors when it is heated. 
One example of such a thermal printing system comprises a facsimile 
apparatus. The present invention in particular relates to a thermal 
printing system having a function for preventing the thermal head from 
being overly heated and having a function for preventing partial loss of 
printed information. Such partial loss of printed information may occur 
because the above-mentioned thermal-head over heating prevention function 
prevents the thermal head from further heated due to excessive rising of 
the temperature of the thermal head being detected. 
In one example of such a facsimile apparatus according to related art, 
temperature detecting means such as a thermistor is provided for detecting 
a temperature of the thermal head. If the detected temperature of the 
thermal head reaches a predetermined value, operation of a printing strobe 
is terminated so as to stop heating of the thermal head. As a result of 
the heating stoppage, overly heating of the thermal head is prevented. 
However, termination of the operation of the printing strobe such as 
mentioned above may result in a partial loss of printed information if the 
printing strobe operation termination occurs in the middle of the printing 
work. On the other hand, it may be possible, in order to prevent the 
termination of the operation of the printing strobe, to provide measures 
for reducing heat load applied to the thermal head while the printing 
strobe is operated. Such measures may comprise, for example, changing the 
resistance value and/or electric current associated with the thermal head, 
and/or adding a heat radiation plate into the thermal head. These measures 
are used for preventing heat from accumulating in the thermal head and 
thus for preventing the thermal head from being overheated. In this 
method, partial loss of printed information can be prevented but the thus 
printed information may become degraded due to insufficient heating of the 
recording (or printing) paper by means of the thermal head. Such 
insufficient heating may result from the above-mentioned reduction of the 
energy supplied to the thermal head. 
Further, in the facsimile apparatus according to the related art, a 
printing strobe-width or strobe time-width (hereinafter used to refer to, 
a time period for which energy is applied to the thermal head) is 
determined in response to the magnitude of the detected temperature of the 
thermal head. Thus, a uniformity in the printing density can be realized 
even though the temperature of the thermal head tends to vary due to 
certain reasons, such as variation in ambient temperature and variation of 
current and/or voltage of the power source used for heating the thermal 
head. 
In this method, however, a problem may occur in a case where a portable 
power source is utilized for heating the thermal head in the facsimile 
apparatus. The problem may occur due to a variation in the current and 
voltage of the portable power source, which variation occurs significantly 
in particular in a power source such as a portable power source. It is 
difficult to maintain a proper printing density only by altering the 
printing strobe time-width to correct the variation in the thermal head 
temperature due to the existence of such a significant variation in the 
current and voltage of the power source for heating the thermal head. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a thermal printing system 
in which the problems mentioned hereinbefore are eliminated. As a result, 
proper protection of the thermal head from over-heating and prevention of 
partial loss of printed information is simultaneously ensured. 
To achieve the object of the present invention, a thermal printing system 
according to the present invention comprises: 
input means for inputting printing data; 
detecting means for detecting a current temperature of a thermal head which 
is used to print information associated with said printing data; 
memory means for storing, instead of printing, said printing data if it is 
determined that said current temperature of said thermal head provided by 
said detecting means results in controlling said thermal head so it is not 
used to print out said printing data. 
The printing data once stored in the memory means is then used to print the 
information associated therewith, the printing being started after the 
current temperature of the thermal head becomes lowered sufficiently. As a 
result, partial loss of printed information can be prevented and better 
printing can be realized. 
Another thermal printing system according to the present invention 
comprises: 
detecting means for detecting a current temperature of a thermal head which 
is used to print information associated with printing data; and 
transfer controlling means for reducing a data transfer rate, at which said 
printing data is transferred from outside to said thermal printing system, 
if the current temperature of said thermal head is in a predetermined 
range. 
The increasing of the thermal head temperature may be controlled due to the 
data-transfer-rate reduction. As a result, partial loss of printed 
information can be prevented and better printing can be realized. 
Another thermal printing system according to the present invention 
comprises: 
detecting means for detecting a current temperature of a thermal head which 
is used to print information associated with printing data; and 
transfer repeating means which, instead of causing other printing data to 
be transferred to said thermal printing system from outside, causes at 
least a last part of once transferred printing data to be transferred 
again, after the current temperature of said thermal head is in a 
predetermined range. 
During the time that the transfer of the other printing data is halted and 
the part of the once transferred data is being transferred again, the 
printing work may be halted. Thus, the increasing of the thermal head 
temperature may be controlled. As a result, by using an appropriate 
printing strobe time-width, better printing is obtained. 
Another thermal printing system according to the present invention 
comprises: 
detecting means for detecting a current temperature of a thermal head which 
is used to print information associated with printing data; and 
strobe controlling means for controlling a strobe time width during which 
said thermal head is heated so as to print the information associated with 
the printing data, the controlling of the strobe time-width being not only 
responsive to the current temperature of said thermal head but also 
responsive to magnitudes of voltage and current of a power source used for 
heating said thermal head. 
The controlling of the printing-strobe time-width responsive to the current 
temperature of said thermal head and responsive to the magnitudes of 
voltage and current of a power source results in the strobe-time 
controlling being carried out properly using information concerning the 
variation in the energy supplied to the thermal head. As a result, it is 
possible to prevent the printing data from being unnecessarily thinned out 
due to the increase in the thermal head temperature. 
Other objects and further features of the present invention will become 
more apparent from the following detailed description when read in 
conjunction with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
An example of a block diagram of a facsimile apparatus of first, second, 
third and fourth embodiments according to the present invention will now 
be described. 
The facsimile apparatus comprises a system control unit or central control 
unit 1 having a ROM comprising a control program and having a RAM to be 
used in the control operation performed by the control unit 1. The 
facsimile apparatus also comprises a plotter unit 2 for printing an image 
according to received data a, the plotter unit 2 comprising, for example: 
a sensor unit for detecting a condition of a recording paper; a thermal 
head for directly printing the image; a thermistor for detecting the 
temperature of the thermal head; a motor for feeding the recording paper 
in the facsimile apparatus. The facsimile apparatus further comprises a 
scanner unit 3 for reading an image to be transmitted to another facsimile 
apparatus. The facsimile apparatus further comprises a memory unit 4 for 
storing read data and/or a received data; and a modem 5 for modulation 
and/or demodulation of data to be transmitted and/or received data. The 
facsimile apparatus further comprises a line control unit 6 comprising a 
network control device and a display unit 7 for displaying information 
concerning the control operation performed in the facsimile apparatus. The 
facsimile apparatus further comprises an operation unit 8 by which an 
operator specifies the operation to be executed by the facsimile 
apparatus. 
An operation flow of a printing control system used in the facsimile 
apparatus of the first embodiment according to the present invention will 
now be described with reference to FIG. 3. 
If a result of a step S1 (the term step will be omitted so that, for 
example, the step S1 will be referred to as simply S1, hereinafter) is 
YES, that is, if data received and then stored in the memory unit 4 
exists, and also if a result of S2 is NO, that is, if the current 
temperature of the thermal head is neither equal to nor above a 
predetermined value, one line of the stored data is printed in S3. One 
line of the stored data corresponds to one line of the previously read 
relevant image data. If a result of S4 is YES, that is, if the data 
reception is finished, and also if a result of S5 is NO, that is, if no 
data received and then stored in the memory unit 4 exists, the operation 
flow of the current cycle is finished. If a result of S1 is NO or if a 
result of S2 is YES, then S4 is executed. Further, if a result of S5 is 
YES, then S2 is again carried out. 
If a result of S4 is NO, that is, if the data reception is not yet 
finished, and if a result of S6 is NO, that is, if one line of data is not 
received, then S1 is again carried out. If a result of S6 is YES, that is, 
if one line of data is received, then S7 is carried out. If a result of S7 
is YES, that is, the current temperature of the thermal head is equal to 
or above the predetermined value, which temperature is detected by the 
thermistor in the plotter unit 2, then data being received is once stored 
in the memory unit 4, in S8. The thus stored data is printed in S9 after 
the current temperature of the thermal head becomes less than the 
predetermined value, that is, the result NO in S7. Thus, the received data 
is stored in the memory unit 4 while the temperature of the thermal head 
is equal to or above the predetermined value, and simultaneously the 
printing speed rate may be substantially controlled. As a result, an 
increase in the temperature of the thermal head is controlled while the 
printing work is carried out. 
In the above mentioned operation flow, the operation of the printing strobe 
is halted when the temperature of the thermal head reaches the 
predetermined value. As a result, the increase of the thermal-head 
temperature is controlled while the printing speed rate is correspondingly 
substantially deteriorated. 
An essential part of an operation flow of a printing control system used in 
the facsimile apparatus of the second embodiment according to the present 
invention will now be described with reference to FIG. 4. 
If a result of S11 is YES, that is, if the thermal-head temperature is 
equal to or above the predetermined value, received data is not used to 
print a corresponding image but is instead once stored in the memory unit 
4 in S12. The thus stored data is used to print the corresponding image in 
S13 after the thermal-head temperature is lowered, that is, after the 
result of S11 becomes NO. In this case, if the printing work were 
continued even though the thermal-head temperature is equal to or above 
the predetermined value, data thinning out would be imposed on the 
received data before this data was used to print the corresponding image 
so as to reduce the load borne by the thermal head. 
In the operation flow of FIG. 4, the starting of the printing work, after 
it is halted in the case where the result of Sell is YES, is carried out 
due to the lowering of the thermal-head temperature. However, this 
starting of the printing work may instead be carried out based on a 
printing ratio, described below, associated with the subsequent line data 
instead of due to the lowering of the thermal-head temperature. The 
printing ratio is a ratio of an area in a unit area on a recording sheet 
on which a change of color is to be performed to another area on which a 
change of color is not to be performed as a result of a printing work 
being performed on the unit area on the recording sheet. 
An operation flow of a printing control system used in the facsimile 
apparatus of the third embodiment according to the present invention will 
now be described with reference to FIGS. 5A and 5B. 
The printing control system of FIGS. 5A and 5B is similar to that of FIG. 
3. However, in the system of FIGS. 5A and 5B, the page of the received 
data is again printed out if the thermal-head temperature becomes equal to 
or above the predetermined value while the relevant page is first being 
printed out. Thus, the printing quality of the relevant page is improved 
even though intermittent printing work, due to the printing work being 
frequently halted in order to control the thermal-head temperature, 
deteriorating the printing quality of the first printed page. 
In FIGS. 5A and 5B, if the result of SD in FIG. 5A is YES, Si of FIG. 5B is 
then executed, and if the result of Se is NO or after Se is executed in 
FIG. 5B, then the current cycle of the operation flow is ended. 
In the operation flow of FIGS. 5A and 5B, the one line of the received data 
is once stored in the memory unit 4 in S.D. Then, if the thermal-head 
temperature is neither equal to nor above the predetermined value, that 
is, if a result of SD is NO, the thus once stored one line of the received 
data is used to print the corresponding one line of the image in S.D. 
Then, if one page of the received data is printed out, that is, if a 
result of S24 is YES, the above-mentioned once stored received data is 
deleted in S.D. Then, if another page of received data exists (YES in 
S26), that is, if the relevant facsimile communication is finished, the 
current cycle of the operation flow is finished. 
If the thermal-head temperature is equal to or above the predetermined 
value (YES in SD), another line of the received data is then stored in the 
memory unit 4 in Si. Then, if storage of the page of the received data is 
completed (YES in S28) as a result of repeated storage of the lines of the 
received data in Si, S29 is carried out. Then, if no other page of 
received data exists (YES in S29) , that is, if the relevant facsimile 
communication is finished, Se is then executed. In Se, it is determined 
whether or not there exists a next communication request. If a next 
communication request exists (YES in Se), then it is determined in S31 
whether or not the thermal-head temperature is equal to or below the 
predetermined value. If the result of S31 is YES, that is, if the 
thermal-head temperature is not more than the predetermined value, the 
above-mentioned stored data is then used to print the corresponding image 
in Se. 
If another page of received data exists (NO in S29), it is determined in 
S33 whether or not the thermal-head temperature is equal to or below the 
predetermined value. If the temperature is equal or below the 
predetermined value (YES in S33), it is determined in S34 whether or not 
the printing out of the received data is finished. If the printing out of 
the received data is not yet finished (NO in S34), the data received and 
then stored is used to print the corresponding image in S35. Then, one 
line of received data is stored in the memory unit 4 in S36. Then, if 
storage of one page of the received data is finished (YES in S37) as a 
result of repeated storage of lines of the received data in S36, S38 is 
then carried out. In S38, it is determined whether or not another page of 
received data exists. If no other page of received data exists (YES in 
S38), that is, the relevant facsimile communication is finished, then S30 
is carried out. 
An operation flow of a printing control system of the facsimile apparatus 
according to the fourth embodiment of the present invention will now be 
described with reference to FIG. 6. 
The printing control system of FIG. 6, in order to carry out a printing 
work with the controlled temperature of the plotter unit 2, causes another 
facsimile apparatus to send printing data at a transmission speed rate 
controlled appropriately. The transmission speed is controlled as a result 
of the facsimile apparatus, which will receive the printing data, sending 
information concerning the communication modem rate corresponding to the 
controlled transmission speed rate to the other facsimile which will send 
the printing data. The sending of this information is carried out before 
the facsimile apparatus, which will receive the printing data, receives 
the printing data. The degree of controlling the transmission speed rate 
depends on the current temperature of the plotter unit 2. 
In FIG. 6, if the thermal-head temperature is neither equal to nor above 
the predetermined value (NO in S41), a modem rate of 9600 bps is set (in 
S42) and then the current cycle of the operation flow is finished. If the 
thermal-head temperature is equal or above the predetermined value (YES in 
S41), it is determined in S43 whether or not the level of the thermal-head 
temperature is equal to or above a predetermined level 1. If the 
temperature level is equal to or above the predetermined level 1 (YES in 
S43), a modem rate of 2400 bps is set (in S46) and then the current cycle 
of the operation flow is finished. If the relevant temperature level is 
neither equal to nor above the level 1 (NO in S43) but if the temperature 
level is equal to or above a predetermined level 2 (YES in S44), a modem 
rate of 4800 bps is set (S47) and then the current cycle of the operation 
flow is finished. If the relevant temperature level is neither equal to 
nor above the level 2 (NO in S44), a modem rate of 7200 bps is set (S45) 
and then the current cycle of the operation flow is finished. 
A protocol sequence of the facsimile apparatus of a fifth embodiment 
according to the present invention will now be described with reference to 
FIG. 2. The abbreviations in FIG. 2 will now be described, and it may be 
helpful for understanding in detail to refer to Index of abbreviations 
used in Recommendation T.30, Appendix II to CCITT (International Telegraph 
and Telephone Consultative Committee) Recommendation T. 30. 
Tx.: Transmitter; 
Rx.: Receiver; 
CNG: Calling tone; 
CED: Called station identification; 
NSF: Non-standard facilities; 
CSI: Called subscriber identification; 
DIS: Digital identification signal; 
NSS: Non-standard set-up; 
TSI: Transmission subscriber identification; 
DCS: Digital command signal; 
TCF: Training check; 
CFR: Confirmation to receive; 
NG: indicating erroneous frame; 
PPS: Partial page signal (indicating an end of an entire page or a partial 
page associated with facsimile information); 
EOP: End of procedure; 
PPR: Partial page request (indicating that the premessage has not been 
received properly and specifying a frame, a correction being necessary to 
be made to a facsimile information field associated with the frame); 
MCF: Message confirmation; 
DCN: Disconnect; and 
PIX: Pixel information. 
In the data transmission example shown in FIG. 2, frames 1, 3 and N(or 255) 
are erroneous frames. As a result, only these frames are retransmitted as 
shown in FIG. 2. An operation according to the fifth embodiment of the 
present invention will now be described. In the operation, further to the 
above-mentioned operation in the above example, frames, which are not 
always erroneous frames, may be retransmitted so as to allow a time during 
which the over-heated thermal head may be cooled as described below. 
The facsimile apparatus of the fifth embodiment has a function of an error 
correction mode (this term will be abbreviated ECM hereinafter) in which 
the facsimile apparatus, which has received printing data erroneously, 
request the other facsimile apparatus which has sent the printing data to 
send the printing data of the frames thereof again, which frames to be 
sent again starting from a frame which has the error. There, the apparatus 
sending the printing data may send a number of data frames once, which 
number should be within a predetermined number. The above predetermined 
number depends on a capacity of a buffer which the apparatus receiving the 
printing data has. The apparatus receiving the printing data informs to 
the other apparatus as to which data frames, among the once sent number of 
data frames, are to be sent again. The facsimile apparatus of the fifth 
embodiment, in order to control the printing speed rate so as to control 
the thermal-head temperature, sends information concerning the frame, a 
group of frames, starting at which frame, should be sent again, to the 
other facsimile apparatus which sent the printing data. The frame 
information which is sent as mentioned above may comprise not only the 
frame really having an error but also a frame not really having any error 
for the purpose of controlling the printing work speed. 
An example of such an operation as in a case where printing data is 
received in ECM will now be described. In this example, a plurality of 
pages of image data is sent in one communication connection session (such 
a function may be called multi-receiving). If the thermal-head temperature 
reaches a predetermined value when the last part of the page of the 
printing data is printed out, the printing work is continued without 
regard-to whether the relevant temperature has reached the predetermined 
value. This predetermined value is a value such that, after the 
thermal-head temperature reaches the value, a predetermined data 
thinning-out printing manner is normally applied to the printing work. 
Then, another page of printing data is not received, and, in order to have 
the time required for lowering the relevant thermal-head temperature, the 
last group of frames of the previous received printing data is sent again. 
Similarly to the above case but where the thermal-head temperature attains 
a second predetermined value lower than the above-mentioned predetermined 
value for the data thinning-out printing manner, the second predetermined 
value being a rather high thermal-head temperature, a next page of 
printing data is not received immediately even though there is not a real 
error in the received data. Instead, the number of frames, which number is 
controlled to correspond to the magnitude of the current thermal-head 
temperature, is sent again in order to have the time required to lower the 
thermal-head temperature. Such an operation will also be performed if the 
rising thermal-head temperature phenomena occurs when the intermediate 
part of the page is printed out. That is, the printing operation is 
continued, until the printing out of the relevant page has been finished, 
without performing the data thinning-out measure. 
There, the re-sent frames of printing data are ignored when those frames of 
printing data includes no erroneous frame. On the other hand, if the 
re-sent frames of printing data include an erroneous frame, the printing 
operation was stopped when the relevant erroneous frame was found. Then, 
the re-sent frames of printing data are used to start printing out a part 
of the relevant image, this part to be printed starting from a position 
which the erroneous frame corresponds to. 
Though the number of frames to be sent again is controlled so as to 
appropriately control the time for halting the printing work in the above 
description, another method may be used for accomplishing the same 
purpose. That is, instead of controlling the number of frames to be sent 
again, a length of each frame to be sent again may be controlled, 
according to the thermal-head temperature when a data receiving process is 
started. In one example of controlling a frame length, a frame length of 
256 bites is controlled to become 64 bites. How the re-sent 
controlled-length frames of printing data are handled is similar to the 
manner as mentioned above regarding the manner in which the re-sent 
not-controlled-length frames are handled. 
A control manner of a thermal printing system of a sixth embodiment 
according to the present invention will now be described. The thermal 
printing system of the sixth embodiment uses a portable power source for 
the power source of the system. The portable power source is a power 
source currently used in so-called note-book type small personal 
computers. Such a power-source comprises a portable converter for 
converting household-use alternating current power into direct current 
power. 
The portable power source has electric current-voltage (referred to I-V 
hereinafter) characteristics such as shown in FIG. 7. In FIG. 7, an a part 
shown by hatching with oblique lines indicates an area within which the 
combination of the voltage and electric current values may lie. Such 
characteristics are determined as a result of a design of the power source 
which achieves a proper protection of the power source in a case where the 
power source is short-circuited for a certain reason. In such a 
short-circuit condition, which makes the voltage V approximately 0, the 
electric current I is reduced (preferably the electric current I should be 
absolutely zero) so as to stop the power supply thereby. 
In the thermal printing system having such characteristics as shown in FIG. 
7 to a remarkable degree, that is, those shown in FIG. 7, the same 
printing pulse time-width (for which an electric current flows through the 
thermal head) being input to the thermal printing system actually results 
in printing densities which vary in accordance with the electric-current 
value. This is because the variation in the electric-current value results 
in the variation in energy (P=IV=IR.sup.2, where I is the electric 
current, V is the voltage, and R is the resistance of the thermal head) 
used for printing out printing data. 
In the thermal printing system of the sixth embodiment according to the 
present invention, the printing pulse width used for heating the thermal 
head so as to print data is determined using not only the thermal-head 
temperature at a printing time but also a printing ratio, such as 
mentioned above, associated with the line printing data to be printed out 
or the actual electric-current value. 
In the case where the printing ratio is used to determine a printing pulse 
width, a printing ratio associated with each block of line printing data 
is used. In an example of this case, when an entire line of printing data 
is printed out at one time, a printing ratio associated with an entire 
line of printing data is used. In a case where a line of printing data is 
printed out two times as a result of dividing the entire line into two 
blocks, two printing ratios associated respectively with the two blocks 
are used. 
Further, it is possible to make a determination, after taking into account 
such conditions, as to whether or not printing data is to be thinned out 
so as to prevent over-heating of the thermal head. That is, the 
above-mentioned determination may be made after taking into account not 
only a thermal-head temperature but also a printing ratio associated with 
the relevant printing data and an electric current required for heating 
the thermal head during printing out the relevant printing data. As a 
result, the data thinning out may be reduced so that such data thinning 
out measure is taken only in a case where this measure is absolutely 
necessary. Thus, the data loss phenomena can be effectively reduced. 
In the thermal printing system of the sixth embodiment of the present 
invention, by taking into account not only a thermal head temperature but 
also taking into account the power-source voltage and electric current, 
variation in strobe energy for a constant period of time can be determined 
so that an appropriate printing pulse width control can be then realized. 
Further, in the thermal printing system of the sixth embodiment of the 
present invention, the power-source voltage and electric current can be 
determined by using a printing ratio of line printing data so that an 
appropriate printing pulse width control can be realized. 
Further, in the thermal printing system of the sixth embodiment of the 
present invention, determination as to whether or not a data thinning out 
measure is to be taken is made using information concerning the 
power-source voltage and electric current. As a result, the data thinning 
out may be effectively reduced so that such data thinning out measure is 
taken only in a case where this measure is absolutely necessary. 
Further, the present invention is not limited to the above described 
embodiments, and variations and modifications may be made without 
departing from the scope of the present invention.