JPS63188063A - Thermal printing control circuit - Google Patents

Abstract

PURPOSE:To contrive a longer life of a thermal head as well as a higher printing speed, by applying a preheating pulse signal to respective heating elements to heat the thermal head to a fixed temperature. CONSTITUTION:In the period that a printing control signal (a) of L level representing a continuous printing action period is inputted, the temperature of a thermal head 13 is kept at nearly a printing optimum temperature Tm. Then, with the change of the printing control signal (a) to H level, which represents that the continuous printing action period came to an end and changed-over to a stand-by period lasting until the start of a next continuous printing action, the temperature of the thermal head 13 is controlled to a preheating temperature Tp (=40 deg.C) substantially higher than a normal temperature Ts (=25 deg.C). Therefore, the thermal head 13 controlled to be at the preheating temperature Tp can be sufficiently increased to the printing optimum temperature Tm (=70 deg.C) with the amount of heat being lower than that required to the increase from the normal temperature Ts (=25 deg.C) directly to the printing optimum temperature Tm (=70 deg.C). At the start of printing a series of bar code, a pulse width T2 of a heating pulse signal (d) can be reduced. In this manner, a paper feed speed of printing paper is increased, which enables the reduction of an H-level period T1 of a printing command signal (b) thereby resulting in the enhancement of a printing speed.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a thermal printer that prints characters or figures, and particularly to thermal printing control that controls the temperature of a thermal head in which a plurality of heating elements are arranged to an optimum temperature. Regarding circuits.

[Prior Art] In a thermal printer that prints characters or figures using a thermal head in which a large number of heating elements are arranged in a row, one of the thermal head and the printing paper is fixed, and the other is equally spaced. While moving at high speed, each heating element constituting the thermal head is energized and heated to print the corresponding character or figure on the printing paper.

In such a thermal printer, in order to obtain good print quality, it is necessary to control the temperature of the thermal head to an optimal value. For example, when printing a barcode as shown in Figure 6 using this thermal printer, the width of the thermal head is set larger than the width of the barcode, and the printing paper is moved in the direction of the arrow in the direction of the barcode. Assume that printing is performed while moving at a constant speed by a distance β. In this case, if the amount of heat generated by each heating element of the thermal head is too large, the distance between the bars constituting the barcode will fall below a standard value, making it impossible to read the barcode correctly. On the other hand, if the heat generation amount of each heating element of the thermal head is too small, the distance between each bar will exceed the standard value, and
Similarly to the above, it becomes impossible to read the barcode correctly.

Also, if the same heating element is heated with electricity for a long time,
Due to the heat storage effect of the thermal head, as shown in FIG. 7, there is a concern that the distance between each bar may change between the mark II start position @A of the barcode and the printing end position B.

In order to avoid such problems, a thermistor 2 for temperature detection is embedded in the thermal head 1 as shown in FIG. A bar code printing device has been proposed in which the pulse width of a heating pulse signal applied to an element is adjusted (Japanese Patent Application No. 6O-54037).

In this barcode printing device, the pulse width of the clock pulse signal CLK input from the outside is controlled by a monostable circuit (
The one-shot multivibrator) 3 changes the temperature in response to the temperature detection signal from the thermistor 2. and,
As a logical product value of the heating pulse signal S1 outputted from the monostable circuit 3 by the gate circuit 4 and the printing command signal S2 corresponding to the bar code distance f11β in one direction of the barcode outputted from the printing control circuit 5. Output. Then, the pulse signal output from the gate circuit 4 is applied as a new heating pulse signal S3 to the common terminal of each heating element of the thermal head 1. By configuring like this,
The density of thermal head 1 during printing is 13!
It is possible to control the temperature to

[Problems to be Solved by the Invention] However, even in the barcode printing device configured as shown in FIG. 8, the following problems still exist. That is, the bar code distance β in one direction from the print control circuit 5 is
When the printing command signal S2 having a period corresponding to 1 is not inputted, naturally the heating pulse signal S3 is not applied to each heating element of the thermal head 1. Therefore, when the printing command signal S2 ends, that is, as shown in FIG. When printing of one barcode shown in is completed, the temperature of the thermal head 1 decreases to below the printing optimum temperature T-. When printing the next barcode, the print control circuit 5 outputs the print command signal S2 again, and when the heating pulse signal S3 is input, the thermal head 1 rises to the original optimum printing temperature T■. .

Generally, when printing figures such as barcodes using a thermal printer, several barcodes of the same shape are printed in units of several pieces. When a series of barcodes with the same code have been printed, the code is changed and several barcodes are printed in succession. With such a printing procedure, during the period when the same barcode is being printed, the time between printing one barcode and the next is very short, so the density of the thermal head 1 will not decrease. Although it is small, the printing standby time from the end of printing a series of barcodes of the same code to the start of printing of the next type of barcode becomes longer. Therefore, during the standby time, the temperature of the thermal head 1 decreases from the printing optimum temperature Tl to the atmospheric concentration near the room temperature T3.

Therefore, each time a series of barcodes of the same type is printed, the temperature of the thermal head 1 changes back and forth between the normal ITs and the optimum printing temperature TI.

For example, if the normal ITs in a thermal printer is about 25°C and the optimum printing temperature TI is about 70°C, the temperature difference is 45°C.
Therefore, the thermal head 1 traces a temperature difference R history of 45° C. every time it prints a series of characters or figures. Therefore, there is a problem that the life of the thermal head is shortened due to thermal fatigue.

Also, each time you start printing one type of character or figure, the temperature of the thermal head is changed from mTs to the optimum printing temperature Tl.
Since it is necessary to raise the temperature to 11, a large amount of heat must be generated in a short time at the start of printing. As mentioned above, increasing the generation rate of the heating element is achieved by increasing the pulse width of the heating pulse signal @S1.
It is difficult to generate a large amount of heat in a short period of time. Therefore, there is an inconvenience that the printing speed must be reduced in order to maintain good print quality.

The present invention was made in view of these circumstances, and
The purpose of this is to apply a preheating pulse signal to each heating element in order to preheat the thermal head to a constant temperature, thereby reducing the temperature difference between a series of printing operations and a standby time when printing is not in progress. An object of the present invention is to provide a thermal printing control circuit that can extend the life of a thermal head and greatly improve the printing speed of characters or figures without deteriorating printing quality.

[Means for Solving the Problems] In the thermal printing control circuit of the present invention, a temperature detector detects the temperature of a thermal head in which a plurality of heating elements are arranged, a temperature detection signal is output, and a pulse generating means generates a basic pulse signal to be applied to each heating element, and a first pulse width control circuit controls the pulse width of the basic pulse signal so that the thermal head reaches the optimum temperature for printing in response to the temperature detection signal. .

Further, a second pulse width control circuit receives the heating pulse signal output from the first pulse width control circuit and controls the pulse width of the basic pulse signal so that the thermal head reaches a preheating temperature lower than the optimum printing temperature. In response to the print command signal, a heating pulse signal output from the first pulse width control circuit is applied to the heating element, and a preheating pulse signal output from the second pulse width control circuit is applied to the heating element. A gate circuit is provided.

[Function] With the thermal printing control circuit configured in this way,
During the sending period of the print command signal, a heating pulse signal having a pulse width that brings the thermal head to the optimum temperature for printing is applied from the first pulse width control circuit to each heating element of the thermal head. Further, a preheating pulse signal having a pulse width such that the thermal head has a preheating temperature lower than the optimum printing temperature is applied from the second pulse width control circuit to each heating element of the thermal head. Therefore, during printing, the temperature of the thermal head is set to the optimum printing temperature of the heating pulse signal with a high control temperature, and during printing standby, the temperature of the thermal head is controlled to a preheating temperature lower than the optimum printing temperature by the preheating pulse signal.

Therefore, there is almost no difference in temperature between printing operation and printing standby.

[Example] An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit diagram showing a thermal printing control circuit according to an embodiment. In the figure, reference numeral 11 denotes a control section formed from, for example, a microcomputer, and print data of characters or figures to be printed is sent from a data terminal of this control section 11 to a data latch circuit 12 of a thermal head 13. The data latch circuit 12 temporarily stores the input print data, and also turns on each data terminal D1 to ON of the thermal head 13.
Apply to.

The thermal head 13 has a circuit configuration shown in FIG. 2, for example. A plurality of heating elements 15 are connected to a power supply terminal with a driving voltage of 10 Vo through switching transistors 14, respectively.
are connected to each other, and a common terminal of each heating element 15 is grounded via a transistor 16. A print data signal is inputted to each base of each switching transistor 14 from each of the data terminals D1 to DN. Further, a heating pulse signal or a preheating pulse signal output from a gate circuit 17 in FIG. 1, which will be described later, is input to the base of the transistor 16.

Roughly speaking, a thermistor 18 as a temperature detector for detecting the temperature of this thermal head 13 is embedded in a support member that fixes and holds each heating element 15 of this thermal head 13.

In FIG. 1, a print start signal is input to the print control circuit 19 from the output terminal G1 of the control section 11.

When the print control circuit 19 receives the print start signal, it inputs a print command signal that remains at H level for the time T1 required to print one character or figure to one input terminal of the AND gate 17a of the gate circuit 17. do. - Furthermore, the control section 11 constitutes a pulse generating means. The clock signal (basic pulse signal C) output from the output terminal CLK of this control section 11 is transmitted to the first pulse width control circuit 2.
The trigger terminal Tr of the first monostable circuit 20d constituting the
1. This first monostable circuit 20d, when the basic pulse signal C is input to the trigger terminal Tr1,
Capacitor 20a externally connected to this circuit from the input time
and a certain time T determined by the time constants of resistors 20b and 20c.
A pulse signal having an H level of 2, that is, a heating pulse signal d, is output from the output terminal Q. The thermistor 18 of the thermal head 13 is connected to both ends of the resistor 20c. Therefore, when the resistance value of the thermistor 18 changes, the pulse width T2 of the heating pulse signal d output from the output terminal Q changes. This first monostable circuit 20d
The heating pulse signal d output from the gate circuit 17
The signal is input to the other input terminal of the AND gate 17a, and is also input to one input terminal of the AND gate 21a constituting the second pulse width control circuit 21.

The basic pulse signal C output from the control section 11 is input to the first monostable circuit 20 (j) and is also input to the second monostable circuit 21 constituting the second pulse width control circuit 21.
b is input to the trigger terminal Tr2. This second monostable circuit 21t) sends a basic pulse signal C to the trigger terminal Tr2.
is input, a pulse signal e is output to the output terminal Q, which remains at the L level for a certain period of time T3 determined by the time constant of the capacitor 21c and resistor 21d externally connected to this circuit from the input time.
to the other input terminal of the AND gate 21a.

The pulse signal output from the AND gate 21a of the second pulse width control circuit 21 is input as a preheating pulse signal to one input terminal of the OR gate 17b of the gate circuit 17 via one input terminal of the AND gate 22. . The other input terminal of this OR gate 17b is connected to an AND gate 1.
The heating pulse signal Q output from 7a is input. The output signal output from the OR gate 17b of the gate circuit 17 is input to the base of the transistor 16 of the thermal head 13.

Roughly speaking, a print control signal a indicating a series of printing operation periods To is inputted from the output terminal G2 of the control section 11 to the other input terminal of the AND gate 22. This series of printing operation period To indicates the time required to print a series of characters or figures when printing a plurality of characters or figures in succession, and is set separately by the operator depending on the number of characters or figures to be printed, for example. It is also possible to set from the operation panel provided.

Next, the operation when printing a plurality of solid bar codes shown in FIG. 3 using a thermal printer incorporating the thermal printing control circuit configured as described above will be explained using the time chart shown in FIG. 4. do.

First, since the basic pulse signal @C having a period T5 is output from the output terminal CLK of the control unit 11, the heating pulse signal d having a pulse width T2 is output from the first monostable circuit 20d. Further, a pulse signal e having a fixed pulse width T3 is output from the second monostable circuit 21b. As a result, the pulse width T4 of the preheating pulse signal t output from the AND gate 21a is equal to the pulse width T4 of the heating pulse signal d.
The pulse width is obtained by subtracting the fixed pulse width T3 of the pulse signal e from 2.

Now, when the print control signal a changes from the H level to the L level at time to, the AND gate 22 enters the cutoff state.

Therefore, the preheating pulse signal f is not applied to the thermal head 13.

Next, at time t1, when the print control signal becomes H level, the heating pulse signal d output from the first monostable circuit 20d is applied to the thermal head 13 via the AND gate 17a and the OR gate 17b of the gate circuit 17. transistor 1
Applied to the base of 6. Therefore, the corresponding heating element 5
is energized and heated by the heating pulse signal d. As a result, the temperature of the thermal head 13 increases. Initially, the temperature of the thermal head 13 is low, so the thermistor 18 controls the pulse width T2 of the heating pulse signal @d output from the first monostable circuit 20d to be wide. When the temperature of the thermal head 13 rises, the thermistor 18 controls the pulse width T2 of the heating pulse signal @d output from the first monostable circuit 20d to become narrower. As a result, the thermal head 1
The temperature of 3 becomes a constant value. The values of the capacitor 20a and the resistors 20b and 20c are adjusted in advance so that the temperature at this constant value becomes the optimum printing temperature Tm (=70° C.). Therefore, as long as the print command signal S maintains the H level, the temperature of the thermal head 13 will be the optimum printing temperature Tm.
(=70°C).

Note that as long as the thermal head 13 maintains a constant temperature, the pulse width T2 of the heating pulse signal d is constant.

Next, when printing of one barcode is completed at time t2 and the print command signal changes to L level, the application of the heating pulse signal d to the thermal head 13 is cut off. Then, the temperature of the thermal head 13 gradually decreases from the optimum printing temperature Tw.

Next, at time t3, when the print command signal S reaches the H level, the heating pulse signal d is again applied to each heating element 15 of the thermal head 13. As a result, the thermal head 13
The temperature rises again to the optimum printing temperature Tll1.

Furthermore, at time t4, the printing operation of a series of barcodes with the same code is completed, and the print control signal a changes from the L level to the H level.
Since the AND gate 22 becomes conductive, the preheating pulse signal is sent to the thermal head 1 via the OR gate 17b of the gate circuit 17 instead of the heating pulse signal d.
3. In this case, initially the thermal bed 13
The temperature is the optimum printing temperature T+a, but since the heating pulse signal d is cut off, the temperature of the thermal head 13 gradually decreases. When the temperature of the thermal head 13 decreases,
Due to the action of the thermistor 18, the pulse width T2 of the heating pulse signal @d is gradually heated with a pulse II T4 adapted to the temperature of the thermal head 13. Then, the preheating temperature Tp is determined by the values of the capacitor 2IC and the resistor 21d.
(-40℃), the thermal head 13
The temperature of becomes constant.

With such a thermal printing control circuit, the temperature of the thermal head 13 is maintained at approximately the optimum printing temperature Tm during the period when the printing control signal a at the L level indicating a series of printing operation periods is input, and the temperature of the thermal head 13 is maintained at approximately the optimum printing temperature Print i! indicates that the operation has finished and a waiting period has begun until the start of the next series of print operations. When the 1IJ111 signal a changes to H level, the temperature of the thermal head 13 is controlled to the preheating temperature Tp (-40°C), which is considerably higher than the room temperature Ts (-25°C).

Therefore, the amount of heat required to raise the thermal head 13 controlled at this preheating temperature Tp to the optimum printing temperature Tm (-70°C) is from normal temperature Ts (-25°C) to -optimum printing temperature Tm ( A small amount of heat is sufficient compared to the heat required to raise the temperature to -70°C. Therefore, the pulse width T2 of the heating pulse signal d applied to each heating element 15 of the thermal head 13 at the start of printing a series of barcodes can be reduced. As a result, it is possible to raise the thermal spatula 13 to the optimum printing temperature TI in a short time, and as a result, by increasing the paper feeding speed of the printing paper, the period of the H level of the print command signal TI is reduced. The time required to print the barcode bar distance β in one direction in Figure 3 can be shortened.
The printing speed of the whole 7 can be greatly improved without deteriorating the printing quality.

The fifth factor is a characteristic diagram showing the relationship between the temperature of the thermal head 13 and the pulse width T2 of the heating pulse signal d that occurs at the start of barcode printing at that temperature. As is clear from the figure, the pulse IIT2 of the heating pulse signal when the thermal head 13 is preheated to 40°C can be significantly shortened compared to the pulse width when the temperature is at room temperature of 25°C.

Furthermore, since the temperature change of the thermal head 13 is reduced, the effect of thermal stress caused by thermal expansion and contraction is reduced, and the life of the thermal head 13 can be significantly extended.

Note that the present invention is not limited to the embodiments described above. In the embodiment, the present invention was applied to a thermal printer that prints barcodes, but it can also be used for a thermal printer that prints ordinary characters and figures.

[Effects of the Invention] As described above, according to the present invention, a preheating pulse signal is applied to each heating element in order to preheat the thermal head to a constant temperature. Therefore, it is possible to reduce the temperature difference between a series of printing operations and when waiting for printing to start the next printing operation, extend the life of the thermal head, and significantly increase the printing speed of characters or graphics without degrading print quality. You can improve.

[Brief explanation of the drawing]

1 to 5 show a thermal printing control circuit according to an embodiment of the present invention. FIG. 1 is an overall circuit diagram, FIG. 2 is a circuit diagram showing a thermal head, and FIG. 3 is a circuit diagram showing a thermal head. The figure shows a barcode, Figure 4 is a time chart showing the operation, Figure 5 is a characteristic diagram to explain the effect, and Figures 6 to 8 explain the conventional barcode printing device. FIG. 6 is a diagram showing a bar code, FIG. 7 is a diagram for explaining problems of the conventional device, and FIG. 8 is a schematic circuit diagram. 11... Control unit, 12... Data latch circuit, 13
...Thermal head, 15...Heating element, 16...
- Transistor, 17... Gate circuit, 18... Thermistor, 19... Print control circuit, 20... First pulse width control circuit, 20d... First monostable circuit, 2
1... Second pulse width control circuit, 21b... Second monostable circuit, b... Print command signal, C... Basic pulse signal, d... Heating pulse signal, f...・Preheating pulse signal. Applicant's agent Patent attorney Takehiko Suzue Figure 5987 Figure 118

Claims (1)

[Claims] a thermal head (13) in which a plurality of heating elements are arranged; a temperature detector (18) for detecting the temperature of the thermal head and outputting a temperature detection signal; and a temperature detector (18) for detecting the temperature of the thermal head and outputting a temperature detection signal; a pulse generating means (11) for generating a basic pulse signal (c); and a pulse width of the basic pulse signal outputted from the pulse generating means so that the thermal head reaches the optimum temperature for printing in response to the temperature detection signal. a first pulse width control circuit (20) that controls the
Pulses of the basic pulse signal outputted from the pulse generation means so that the thermal head receives the heating pulse signal (d) outputted from the first pulse width control circuit and reaches a preheating temperature lower than the optimum printing temperature. The second to control the width
a pulse width control circuit (21), which applies a heating pulse signal outputted from the first pulse width control circuit to the heating element in response to the print command signal (b), and controls the second pulse width. Preheating pulse signal output from the circuit (
A thermal printing control circuit comprising: a gate circuit (17) for applying f) to the heating element.