BACKGROUND OF THE INVENTION
[0001] The present invention relates to a thermal printing apparatus for using a line thermal
head.
[0002] In a conventional thermal printing apparatus using a line thermal head, since the
printing width is kept constant and a continuous thermal sensitive paper is used in
correspondence with said printing width, the widthwise non-printed area of the thermal
sensitive paper depends upon the size of the original. To reduce the resulting waste
of paper, on copying small width original various sizes of separated papers may be
used.
[0003] In the line thermal head, in accordance with a content of the original or an output
signal of the printing pattern, it is possible to determine which elements of the
line thermal head should be heated. However, if a piece of cut paper is used and the
size of the paper is selected in error, the width of printing pattern may be larger
than expected. In this case, the heating elements which are located outside of the
printing width of paper are also heated. Even if the size of paper is selected correctly,
it often happens that the width of the printing pattern is as long as the width of
paper but that the whole position of the printing pattern signal is slightly offset
in the lateral direction. In this case, the heating elements located outside the width
of the paper are also heated.
[0004] Heating elements that are heated without thermal sensitive paper being under them
become over-heated and are said to be in a state of "idle heating". Further, if the
elements are over-heated repeatedly, the elements are likely to be damaged or break
down. Further, if the heating elements which are located close to the edges of paper
are repeatedly over-heated, these heating elements are readily damaged with the result
that there is a blank line on the printed surface of full width papers in the longitudinal
direction.
[0005] In this case, it is very difficult to replace only the broken and damaged elements
of the line thermal head by new ones. Accordingly, the whole head must be exchanged
by new head. Therefore, although the waste of paper is reduced by using paper of narrow
width for small width originals, the cost of maintenance is increased. Also, in the
case of using cut paper, there is the fear that a printing signal will be inputted
into a control means for the line thermal head so that the heating elements thereof
are accidentally subjected to heat before the paper has arrived at said line thermal
head and remain energized after the paper has passed said line thermal head. This
is also known as "idle heat".
[0006] EP-A-181 064 is a prior art that has given thought to some of the above problems.
It discloses a fixed head type thermal printer having a plurality of dot printing
elements defining a line of print. This printer has means for supplying power sequentially
to blocks of said elements, the exact number being determined in accordance with the
number of dots to be printed. Of interest is the fact that this known apparatus includes
means for detecting the width of the paper moving past said elements and serving to
prevent the supply of power to elements positioned adjacent to areas in which said
paper is absent. In the particular embodiment of this prior art a handwheel is used
to adjust the spacing between two pin tractors to a setting in which they mate with
the pin holes in a selected roll width of printing pager. This adjustment rotates
a rotary encoder to a setting controlling a de-energizing circuit such that all strobe
terminals that are positioned beyond the width of the paper from said roll are not
capable of being energized.
SUMMARY OF THE INVENTION
[0007] It is an object of the present invention to provide a thermal printer including a
line thermal head and with which a plurality of different sizes of cut paper can be
used without any fear that this will result in heating elements in the line thermal
head becoming over-heated due to paper widths being used that are less than the width
of the line thermal head and due to spaces that may be present between the trailing
edge of a leading sheet and the leading edge of the next successive sheet passing
under the line thermal head, and thus to prolong the life of the line thermal head.
[0008] This and other objects are attained by providing a thermal printer including a line
thermal head having heating elements, comprising:
means for receiving thermal sensitive cut papers having a plurality of sizes;
means for selectively feeding said papers from said receiving means to said thermal
head;
electric power supply means for supplying electric power to said heating elements;
and
control means for controlling said power supply from said electric power supply
means in response to a size of the selected papers, said control means including means
for preventing said power supply to a part of said heating elements located in a predetermined
width on each side of said line thermal head in response to a width of the selected
papers whereby any waste idle heat of said heating elements may be avoided;
said control means including detecting means provided on an inlet side of said
line thermal head and generating a detection signal for a first period of time commencing
from the detection of the leading end of a sheet of paper; and generating a detection
signal for a second period of time commencing from the detection of the trailing end
of said sheet of paper; said control means being such that it causes energization
of said heating elements at the end of said first period of time and causes de-energization
of said heating elements at the end of said second period of time.
[0009] When cut papers are used, paper is not continuously below the thermal head. After
a sheet of paper has passed through the thermal head, there is no paper below the
thermal head until the next sheet passes through. Therefore, the heating elements
of known thermal printers are idle-heated by flowing current unnecessarily to the
thermal head until the next sheet of paper is fed below the thermal head.
[0010] In the present invention, the paper is detected at the inlet side of the line thermal
head and the line thermal printer prevents the current from flowing through the line
thermal head before a lapse of a predetermined time lag from a time when a detection
signal has been generated. Therefore, there is no problem that the heating elements
are idle-heated. In the same way, with respect to the trailing edge of the paper,
since the thermal printer prevents a current from flowing through the thermal head
after another predetermined time lag from a time when the detection signal has been
terminated.
[0011] With respect to the width of the paper, the thermal printer of the present invention
prevents current from flowing to those elements of the line thermal head under which
there is no paper passing. Therefore, there is no problem that heating elements of
the line thermal head will be idle-heated.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] In the accompanying drawings:
Fig. 1 is a diagram showing a thermal printer according to an embodiment of the present
invention; and
Fig. 2 is a circuit diagram showing primary portion of the embodiment.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0013] Fig. 1 shows a whole system of a thermal printer according to one embodiment of the
present invention. In Fig. 1, reference characters A3, A4, B4, and B5 representative
of various sizes denote trays for receiving thermal sensitive cut papers. The trays
are inserted into shelves provided in a printer body. Papers A3, A4, B4, and B5 are
received in the trays A3, A4, B4 and B5, respectively.
[0014] Reference characters P1, P2, P3 and P4 indicate limit switches for detecting sizes
of the trays inserted in the printer body. If the tray is inserted into the printer
body, the associated limit switch is turned on. Feeding rolls r1, r2, r3 and r4 are
each provided in contact with a printing surface of the thermal sensitive paper received
in each tray. The feeding rolls are operated, respectively, by a signal fed from a
control unit 2 (later described) for feeding papers.
[0015] A pair of nip rolls 10 are provided in the midway of a paper feed path from each
tray to the printing position. The nip rolls 10 are provided to operate at once.
[0016] A pair of the nip rolls 11 are commonly used for each size of paper. The nip rolls
11 are provided on an inlet side of the paper to the printing position.
[0017] A printing unit includes a line thermal head 12, and a platen roll 13. The line thermal
head 12 is normally lifted away from the platen roll 13. The line thermal head 12
is driven so that the head 12 is lowered only when the paper passes below the head
12.
[0018] A pair of nip rolls 14 are used for discharging the paper. The paper is fed along
a paper path 20. A light emitting element 15 and a light receiving element 16 are
provided between the nip rolls 11 and platen roll 13. The light emitting element 15
and light receiving element 16 are provided to face each other across the passage
20 so as to detect the existence of the paper.
[0019] A cable 1 is used for interconnecting a computer and a printer to each other. A computer
(not shown) applies signals of the printing pattern. The control unit 2 is used to
select one signal for designating the size of the paper and the other signal for a
printing pattern image in accordance with the signals fed from the computer. Both
kinds of the signals are restricted by the computer so that the size designation signal
is first outputted and subsequently the image signal is outputted therefrom. The control
unit 2 serves to select the size designation signal, to judge the designated size,
to store it, to feed a suitable signal to a paper feed control unit 5, to temporarily
drive the feed roll (any one of rolls r1 to r4) corresponding to the signal sensitive
paper where the paper reaches the nip roll 10.
[0020] All of the nip rolls 10, 11, and 14 are simultaneously rotated and the thermal sensitive
paper is fed until the paper is discharged by the nip rolls 14. During this operation,
when the paper has passed below the element 16, the incident light is blocked off
by the paper so that the light receiving element 16 outputs the signal for detecting
the paper. The control unit 2 detects an initial rise of the blocking signal. After
the predetermined time lag longer than required for the leading edge of the thermal
sensitive paper to enter between the thermal head 12 and the platen roller 13, the
thermal head 12 is lowered so that the signal is fed to the computer to allow the
issuance of the print pattern image signal from the computer. Thereafter, the image
signal is sent from the computer so that the thermal head is energized to start the
printing operation.
[0021] When the trailing edge of the paper has passed below the light receiving element
16, no signal for detecting the paper is issued. When this state is detected by the
control unit 2, after a predetermined time lag the image signal issuance is stopped
to interrupt the energization of the thermal head 12. If the printing is continued,
the signal for continuing the printing is sent from the computer. The control unit
2 operates to repeat the above-mentioned operation in accordance with the signal which
is sent from the computer.
[0022] Fig. 2 shows a circuit for setting a heating preventing zone for preventing the thermal
head from being heated at both end portions. Reference character T shows respective
heating elements each of which is connected to one thermal of a power source through
a gate element g. A number of heating elements which are arranged in the unit portion
of the width of the to-be-used paper having the smallest size are connected directly
to the other terminal of the power source. All the rest elements of both the sides
of the thermal head are divided into several groups and are connected in the last-mentioned
terminal of the power source through the switch elements S1 to S3 of every group.
Reference character B shows a buffer register picking up image signal for one line.
A latch circuit R reads the output of the buffer register B by reading pulses. The
gate elements g are opened or closed in accordance with the signal of the image. As
a result, the current flows to the predetermined heating elements. If the control
unit 2 selects and judges the signal for designating the size, switch elements are
selectively turned on according to the designated size. For example, if the size is
A3, the current flows through all the switch S1 to S3, if the size is B4, the current
is shut off only by switch S1, if the size is A4, the current is shut off by switches
S1 and S2, and if the size is B5, the current is shut off by all the switches S1 to
S3. Such a selected ON/OFF condition is held until a series of the printing operations
have been finished.
[0023] According to the embodiment of the present invention, the tray A3, A4, B4, and B5
can be inserted into the same portion of the printer body as desired. Therefore, the
apparatus can be made compact. In this case, a limit switch is available for feeding
a suitable signal of the paper size.
[0024] In the prior art, a continuous thermal sensitive paper has been used by the printer
having a line thermal head. Therefore, the size of the printing pattern is often less
than the width of paper and thus results in waste paper. However, according to the
present invention, cut paper can be used, since the size of the paper can be selected
in accordance with the width and length of the printing pattern. Therefore, waste
paper can be decreased. It is also possible to reduce maintenance costs for the printer
without any fear that the serving life of the thermal head will become short.
1. A thermal printer including a line thermal head (12) having heating elements (T),
comprising:
means (A3, A4, B4, B5) for receiving thermal sensitive cut papers (A3, A4, B4,
B5) having a plurality of sizes;
means (5) for selectively feeding said papers from said receiving means to said
thermal head (12);
electric power supply means for supplying electric power to said heating elements
(T); and
control means (2) for controlling said power supply from said electric power supply
means in response to a size of the selected papers, said control means (2) including
means for preventing said power supply to a part of said heating elements (T) located
in a predetermined width on each side of said line thermal head in response to a width
of the selected papers whereby any waste idle heat of said heating elements may be
avoided;
said control means (2) including detecting means (16) provided on an inlet side
of said line thermal head (12) and generating a detection signal for a first period
of time commencing from the detection of the leading end of a sheet of paper; and
generating a detection signal for a second period of time commencing from the detection
of the trailing end of said sheet of paper; said control means (2) being such that
it causes energization of said heating elements (T) at the end of said first period
of time and causes de-energization of said heating elements (T) at the end of said
second period of time.
2. The thermal printer according to the Claim 1, wherein said detector means includes
a light source (15) and an optical sensor (16), said light source and said optical
sensor being provided facing each other across a path along which said paper sheets
are conveyed.
1. Thermodrucker, enthaltend einen Zeilen-Thermokopf (12) mit Heizelementen (T), umfassend:
eine Aufnahmeeinrichtung (A3, A4, B4, B5) für geschnittene wärmeempfindliche Papierbögen
(A3, A4, B4, B5) in mehreren Größen;
eine Einrichtung (5) zum selektiven Zuführen der besagten Papierbögen von der besagten
Aufnahmevorrichtung zu dem besagten Thermokopf (12);
eine elektrische Stromversorgungseinrichtung, um die besagten Heizelemente (T)
mit elektrischem Strom zu versorgen; und
eine Steuereinrichtung (2), um die besagte Stromversorgung von der besagten Stromversorgungseinrichtung
ansprechend auf eine Größe der gewählten Papierbögen zu steuern, wobei die besagte
Steuereinrichtung (2) eine Einrichtung einschließt, um die Stromversorgung zu einem
Teil der besagten Heizelemente (T), die in einer vorbestimmten Breite auf jeder Seite
des besagten Zeilen-Thermokopfes angeordnet sind, ansprechend auf eine Breite der
gewählten Papierbögen zu unterbinden, wodurch jegliche vergeudete Leerlauf-Wärme der
besagten Heizelemente vermieden werden kann;
wobei die besagte Steuereinrichtung (2) eine Erkennungseinrichtung (16) einschließt,
die auf einer Einlaßseite des besagten Zeilen-Thermokopfes (12) vorgesehen ist und
ein Erkennungssignal für einen ersten Zeitraum erzeugt, der mit der Erkennung des
vorderen Endes eines Blatts Papier beginnt; und ein Erkennungssignal für einen zweiten
Zeitraum erzeugt, der mit der Erkennung des hinteren Endes des besagten Blatts Papier
beginnt; wobei die besagte Steuereinrichtung (2) derart ausgebildet ist, daß sie eine
Stromführung der besagten Heizelemente (T) am Ende des besagten ersten Zeitraums verursacht,
und ein Abschalten der besagten Heizelemente (T) am Ende des besagten zweiten Zeitraums
verursacht.
2. Thermodrucker nach Anspruch 1, dadurch gekennzeichnet, daß die besagte Erkennungseinrichtung
eine Lichtquelle (15) und einen optischen Sensor (16) einschließt, wobei die besagte
Lichtquelle und der besagte optische Sensor einander über einen Weg gegenüberliegend
vorgesehen sind, entlang dessen die besagten Papierblätter transportiert werden.
1. Imprimante thermique comportant une tête thermique en ligne (12) ayant des éléments
chauffants (T) comprenant :
un moyen (A3, A4, B4, B5) pour recevoir des papiers découpés thermosensibles (A3,
A4, B4, B5) ayant une multitude de formats ;
un moyen (5) pour avancer sélectivement lesdits papiers à partir dudit moyen de
réception vers ladite tête thermique (12) ;
un moyen d'alimentation électrique pour alimenter en énergie électrique lesdits
éléments chauffants (T), et
un moyen de commande (2) pour commander ladite alimentation à partir dudit moyen
d'alimentation électrique en réponse à un format des papiers sélectionnés, ledit moyen
de commande (2) comportant un moyen pour empêcher ladite alimentation à une partie
desdits éléments chauffants (T) placée dans une largeur prédéterminée sur chaque côté
de ladite tête thermique en ligne, en réponse à une largeur des papiers sélectionnés
d'où il résulte que tout chauffage inutile desdits éléments chauffants peut être évité
;
ledit moyen de commande (2) comportant un moyen de détection (16) prévu sur un
côté entrée de ladite tête thermique en ligne (12) et produisant un signal de détection
pendant un premier intervalle de temps commençant à partir de la détection du bord
avant d'une feuille de papier ; et produisant un signal de détection pendant un second
intervalle de temps commençant à partir de la détection du bord arrière de ladite
feuille de papier ; ledit moyen de commande (2) étant tel qu'il provoque l'alimentation
desdits éléments chauffants (T) à la fin du premier intervalle de temps et provoque
la désalimentation desdits éléments chauffants (T) à la fin du second intervalle de
temps.
2. Imprimante thermique selon la revendication 1, dans laquelle ledit moyen de détecteur
comporte une source de lumière (15) et un capteur optique (16), ladite source de lumière
et ledit capteur optique étant prévus en regard l'un de l'autre à travers un trajet
suivant lequel lesdites feuilles de papier sont transportées.