JPS6122639B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a thermal head having a continuous heating element, and particularly to a method of configuring a matrix and a driving circuit thereof.

[Conventional technology]

In a conventional thermal head having a continuous heating element of this type, the diode matrix section has a structure as shown in FIG. In the figure, 1 to 36 are heating elements, 37 to 54 are source side isolation diodes, 55 to 73 are sink side isolation diodes, and 74 are
79 are source side lead terminals (input side lead terminals), and 80 to 87 are sink side lead terminals (output side lead terminals).

Next, the operation will be explained.

In FIG. 1, when each heating element 1 to 36 generates heat, image signals are temporarily stored in the source side lead terminals 74 to 79, and in synchronization with this, the sink side lead terminals 80 to 87 are sequentially turned on. , just turn it off. For example, source side lead terminal 74~
Of the 79 image signal information, terminals 74, 77, 78
Assuming that the terminals 75, 76, and 79 are at the H level and the terminals 75, 76, and 79 are at the L level, the heating elements 1, 32, and 33 generate heat by turning on the sink side lead terminal 80. Next, a new image signal is temporarily stored in the source side lead terminals 74 to 79, and the sink side lead terminal 81 is turned on. For example, among the image signal information of the source side lead terminals 74 to 79, terminals 75 and 7
7, 79 are at H level, terminals 74, 76, 78 are at L level.
level, the sink side lead terminal 81
By turning on heating elements 3, 19, 35
generates a fever.

In this way, the image signal is input to the source side input terminal 74 every time.
79 and sequentially turn on and off the sink side lead terminals 80 to 87, the temperature of any of the heating elements 1 to 36 on the continuous heating element is controlled to increase. At this time, the isolation diodes 37 to 73 serve to prevent reverse current from flowing to the common leads on the source and sink sides.

[Problem that the invention seeks to solve]

As shown in Figure 1, in a conventional thermal head with a continuous heating element of this type, a separation diode is always installed in the opposing leads of each heating element in order to prevent reverse current flowing to the source side lead and sink side lead. In the end, approximately the same number of isolation diodes as the number of heating elements are required. Further, not only in a thermal head having a continuous heating element but also in a normal type, the number of diodes required to be installed is equal to the number of heating elements.

And as a solution to this problem,
Conventionally, as shown in Japanese Patent Application Laid-Open No. 52-119946, for example, a high potential is applied to one common lead, a low potential is applied to the selected one of the other common leads, and an intermediate potential is applied to the unselected one. There is something I did. However, in the thermal head described in the above-mentioned conventional publication, a high potential and an intermediate potential are applied to two common leads located on both sides of the heating element array, respectively, so two power supplies are required, resulting in an increase in size and a complicated structure. However, there are problems in that the drive system is mounted on an insulating substrate, which is a big problem especially when the drive system is mounted on an insulating substrate.

This invention was made in order to eliminate the drawbacks of the conventional devices as described above, and provides a thermal head that can reduce the number of wraparound prevention diodes without increasing the size, complicating the structure, and increasing costs. is intended to provide.

[Means for solving problems]

Therefore, the present invention aims to operate a thermal head having a continuous heating element by alternately applying a drive potential to odd-numbered and even-numbered common leads on the input side. A driver circuit that holds the common lead at a potential level-shifted from the drive potential to a lower potential side, and a switch circuit that selectively holds each output side common lead at either the ground potential or the drive potential are provided. It is something that

[Effect]

In this invention, the odd-numbered and even-numbered input common leads are alternately applied with a driving potential, and the output common leads are held at a ground potential or a driving potential, so that each heat generated When the element is selectively heated, the input side common lead when not in operation is held at a predetermined low potential that is level-shifted from the drive potential, and in this way, the input side common lead is held at a predetermined low potential that is level-shifted from the drive potential. Since it is sufficient to apply a low potential, only one power supply is required.

〔Example〕

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

2-6 illustrate a thermal head according to one embodiment of the present invention. In Figure 2, 1 to 3
6 is a heating element, 55 to 73 are sink side isolation diodes, 74 to 79 are source side lead terminals, 80 to
87 is a sink side lead terminal. This circuit is unchanged from the conventional circuit shown in FIG. 1 except for the removal of the source side isolation diode.

FIG. 3 is an equivalent circuit of a part of the circuit shown in FIG. 2, taking into account the reverse current to the source side lead, and ignoring the influence of the reverse current due to the insertion of a separation diode on the sink side.

Figure 4 is a timing chart showing the correlation between the voltages applied to the source side lead terminal and the sink side lead terminal.The input of the image signal is divided into two systems, and the source side lead terminals 74, 76, and 78 are synchronized. are simultaneously input, and the source side lead terminals 75, 7
7 and 79 are synchronously inputted at the same time, and are not inputted to each system at the same time.

FIG. 5 is a block diagram of each circuit for driving the continuous heating element shown in FIG. 2, and FIG. 6 is a circuit example of the driver circuits 105 and 106 in the block diagram shown in FIG.

Next, the operation will be explained.

In FIG. 2, H is connected to the source side lead terminal 76.
signal, send an L signal to the sink side lead terminal 80,
Assume that the target heating element 17 is caused to generate heat. An equivalent circuit around the heating element 17 at this time is shown in FIG. A current flows through the heating element 17 between 76 and 80, generating sufficient energy to generate heat. In this case, the current flows through the terminals 76→77→32→80, and the voltage drop between the terminals 76 and 77 is small, causing the heating element 32 to generate heat, thereby losing its function as a thermal head.

Therefore, in this embodiment, the even numbered terminals and the odd numbered terminals among the source side lead terminals are operated alternately, and when the even numbered lead terminals are being driven, the odd numbered side lead terminals are held at a certain appropriate level. When the odd-numbered terminals are being driven, the even-numbered terminals are held at a certain appropriate level to prevent unintended heating elements from generating heat.

For example, if the resistance value of any heating element is 400Ω,
It is assumed that the heating element generates sufficient heat when 0.5W is applied, insufficient heat is generated when 0.2W or more is applied, and no heat is generated when 0.2W or less is applied. The current flowing through the heating element when it generates sufficient heat is i=√0.5400, and i=
It becomes 0.035A. Therefore, the current when no heat is generated is i=√0.2400=0.022A, and when no heat is generated, the current must be kept below 22mA.

In this embodiment, the above-described driving method is realized with a configuration as shown in FIG. Further, FIG. 4 shows a timing chart showing the order of these drives. FIG. 4A shows the image signal selection switch 10.
9, and the numbers 80 to 87 in the figure clarify the correspondence with each switch. B and C in the same figure are the output waveforms of the driver circuits 105 and 106, and D and E in the same figure are the output waveforms of the latches 103 and 104.

In FIG. 5, first, (m+n) image signals are stored in shift registers 101 and 102 by a well-known method, and the image signal selection switch 80 constituting the switch circuit is turned on. Next, shift register 101
An image signal is applied to the output of the latch 103, and the driver circuit 105 is driven depending on the state of the image signal.
FIG. 6 shows an example of the circuit configuration of the driver circuit.
In FIG. 6, by inputting the latch output to 1N, a binary state of H level and M level is created according to the effect of the level shifting Zener diode. Therefore, if the output of the latch 103 is at H level, OUT of the driver circuit 105 becomes approximately the same value as Vcc and becomes H level. Also, the output of the latch is L.
level, OUT of the driver circuit 105 shows approximately the Zener potential, and in this way, the output of the driver circuit 105 becomes equal to the power supply voltage Vcc when there is an image signal input, and becomes the Zener potential when there is no image signal input. . In this example, the Zener potential was set to 5V.

Next, the latch output is reset and the image signal state stored in the shift register 102 is applied to the output of the latch 104. Depending on the output state of latch 104, driver circuit 106
Similar to 05, it produces a binary state. Then latch 1
04 is reset, and then the 8ch image signal selection switch 80 is turned OFF. Using similar means, turn on and off the image signal selection switches 81 to 87,
One line of printing is completed.

By the way, in the equivalent circuit shown in FIG. 3, when considering the case where the heating element 17 generates heat, the driver side lead terminal 76 becomes H level and the terminal 77 becomes M level. Terminal 78 is at L level, and terminal 79 is also at L level.
Assume level. Also, the image signal selection switch 10
9 is closed and connected to GND. The appropriate power supply voltage at this time is 14V since 0.5W is applied to the heating element 17. Therefore, the heating element 17 generates sufficient heat. Also, since the terminal 77 is at Zener potential, the heating element 32 has 5V/400Ω=
Only a current of 12.5mA flows, and no heat is generated. Regarding other heating elements 18 to 31, the potential difference between terminals 76 and 77 is 9V, and the current flowing through each heating element is 9V/800Ω=
No heat is generated at around 11.2mA.

By doing so, even if the number of image signal selection switches 109 is increased, sufficient functionality can be achieved by considering the current capacity of the transistor (Tr ₂ ) and Zener diode of the driver circuit.

In addition, in the above embodiment, the image signal selection switch is
I set it to 8ch, but any channel is fine. As another embodiment of this invention, the image signal selection switch is set to 4ch.
Figure 7 shows the case where
As shown in Fig. 9. In FIG. 7, 88 to 97 are source side lead terminals, and 111 to 114 are sink side lead terminals.

In the above embodiment, the level was set to 5V using a Zener diode, but the M level was lower than the H level, and the L level was lower than the H level.
An appropriate potential above the level is sufficient.

〔Effect of the invention〕

According to this invention, since there are two image signal input systems, the printing speed is twice that of the conventional system, but only one power supply is required, and the diode on the source side can be removed, reducing the total number of diodes that generate heat. Since the number of elements is approximately half, it is possible to construct a compact and inexpensive thermal head.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a diode matrix of a conventional thermal head having a continuous heating element, FIG. 2 is a block diagram of a diode matrix of a thermal head having a continuous heating element according to an embodiment of the present invention, and FIG. is an equivalent circuit diagram when the source side diode of the continuous heating element is removed in one embodiment of the present invention,
FIG. 4 is a timing chart of each drive circuit in one embodiment of the present invention, FIG. 5 is a block diagram of each drive circuit in one embodiment of the present invention, and FIG. 6 is the driver circuit shown in FIG. 5. FIG. 7 is a matrix configuration diagram showing another embodiment of the present invention, and FIGS. 8 and 9 are equivalent circuit diagrams of FIG. 7, respectively. In the figure, 74 to 79 are source side lead terminals, 80
~87 are sink side lead terminals, 101 and 102 are shift registers, 103 and 104 are latches, and 10
5, 106 is a driver circuit, 107 is a continuous heating board, 108 is a sink side diode matrix,
109 is an image signal selection switch. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (1)

[Scope of Claims] 1. A heating element group consisting of n heating elements arranged adjacent to each other, and a set consisting of two adjacent heating elements of the heating element group, and both of the heating elements in the set. A plurality of input-side common leads in which the input ends of heating elements are connected to each other, and each connection point is connected to m pieces at every other connection point, and one from each set of four heating elements in two adjacent sets. 2m output side common leads, in which the output ends of the two adjacent heating elements taken out are connected to each other, and each connection point is sequentially connected every 2m via a loop prevention diode, and the above-mentioned plurality. The odd-numbered and even-numbered common leads on the input side are operated by applying a driving potential alternately, and the input common lead when not in operation is leveled to the lower potential side by a predetermined value. A thermal head comprising: a driver circuit that holds the output at a shifted potential; and a switch circuit that selectively holds each of the plurality of output common leads at either the ground potential or the drive potential.