JPH0351146A - Thermal head energization control circuit - Google Patents

Abstract

PURPOSE:To maintain applied energy to a heat generating element at a constant level and make print density constant by entering a temperature near the heat generating element and the voltage of a power supply in a calculation section and calculating time required for energization to the heat generating element. CONSTITUTION:An A/D converter 30 has two functions as a voltage detection device for detection of a power supply 7 voltage and a temperature detection device for detection of a temperature(the voltage of a thermistor 22) near a heat generating element 18. An output from the A/D converter 30, that is, the voltage V of the power supply 7 during electric discharge is read by CPU1. Then energy E applied to the heat generating element 18 is obtained from a table of ROM2 based on the voltage V, a temperature near the heat generating element 18 which is read earlier than the voltage V and the average resistance value of the heat generating element 18. An optimal energization time (t) required for energization to the heat generating element 18 is calculated by t = RE/V<3>. Thus the energy applied to the heat generating element 18 is maintained at a constant level and thereby print density is made uniform.

Description

[Detailed description of the invention] Industrial applications The present invention relates to a thermal head energization control circuit.

Prior Art First, a conventional example is shown in FIG. 1 is the CPU which is the calculation unit
This CPU includes a ROM2 containing a program and a character generator, a workpiece r<A M3 used in the program, and a paper that optically detects printing paper (not shown) and outputs an electrical signal. A human powered boat 5 to which a feed control sensor 4 is connected, an external interface 6 for inputting print data, a head drive circuit 8 to which a power supply 7 is connected, and a motor drive to which a pulse motor 9 for feeding print paper is connected. A circuit IO, a print buffer +1 for storing print data, an output port 12, a Δ/D converter 13, an input port 14, a first 0 counter 15, and a second counter 16 are connected.

The thermal head 17 has a substrate 21 provided with a large number of heating elements 18, a shift register 19 for inputting print data, and a latch 20 for holding print data. The time during which electricity is applied to the heating element 18 means that the CP
It is controlled by a signal output from Ul. Further, the substrate 21 is provided with a thermistor 22 which is a temperature measuring element located near the heating element 18, and a switch 23 which sets the average resistance value of the heating element 18 in a plurality of stages. The thermistor 22 is connected to the midpoint of a voltage dividing resistor 24 and a voltage dividing resistor 25, and is also connected to the A/D converter 13.

This A/D converter 13 is a temperature detection means that converts the output of the thermistor 22 (temperature near the heating element 18) into a digital signal, and is connected to the input terminal of the CI) Ul. A plurality of contacts of the switch 23 are connected to the pull-up resistor 26 and to the input port 14, respectively. That is, this input port 14 detects the average resistance value of the heating element 18 set by the operation of the switch IO and outputs the C
I) This is a resistance value detection means that connects to LJ1.

Next, the operation will be explained with reference to the timing chart shown in FIG. 7 and the flow chart shown in FIG. 8. first,
The average resistance value of the heating element 18 is set by operating the switch 23. This average resistance value is read into the CPUI. Further, the printing cycle 'I' for one line starts when an interrupt of the 10th counter 15 occurs, and the printing cycle T is constant. Here, the operation from point A to point 13 shown in the timing chart of FIG. It will be done. Next, the applied energy E to the heating element 18 is determined from the table in the ROM 2 based on the c'> iJ degree data, and based on this applied energy E, the average resistance value R of the heating element 8, and the voltage V of the power source 7. The time period for energizing the heating element 18 is calculated by the CPUI. This arithmetic formula is SI=RE/V". Subsequently, the print data of the next line is transferred to the shift register 19 of the thermal head 17, and when an interrupt of the first counter 15 occurs, the pulse motor 9 is activated. It is driven for one line and the printing paper is fed.Then, the obtained energization time is set in the second counter 16, and the C
A signal ENI3=O is output from P LJ '1, and a voltage of the power source 7 is applied to the heating element 18 by this signal. That is, printing is performed. Then, at 11.1, when an interrupt from the second counter 1G occurs after a time
) Signal +, 7ENB=1 is output from U1, and the current supply to the heating element 18 is cut off by this signal. ” second is A
The printing cycle T for 1 line extends from time point to time point 8, and this printing cycle T is repeated every time one line is printed.

Problems to be Solved by the Invention Conventionally, it has been assumed that the voltage V of the thermal head 17 source 7 is constant, but in the line type thermal head 17, the heating element 18 is Sometimes the number of dots to be applied is one, and sometimes there are many, resulting in extremely large fluctuations in the load. In order to suppress fluctuations in the voltage V even under the maximum load, a power supply with a larger capacity than the average load is required. If you use a power source with insufficient capacity or a battery whose voltage drops as it discharges, the heating element)
Even if the energization time is calculated, the applied energy E will be insufficient due to the decrease in the power supply voltage V, and the printing density will be poor. This is especially true when printing barcodes with many thick lines.

Means for Solving the Problems A power supply is connected to the heating element of the thermal head, and a temperature detection means including a temperature measuring element located near the heating element and a voltage detection means connected to the power supply are input to a calculation unit. A head drive circuit is connected between the output side of the arithmetic unit and the power source, and the temperature near the heating element detected by the temperature detection means and the temperature detected by the voltage detection means are connected to the power source. The voltage of the power source is inputted to the calculating section to calculate the time period for which the heating element is energized.

Even if the voltage of the working power source changes, it is possible to calculate the accurate energization time to the heating element by taking into account the change in the voltage input from the voltage detection means, and therefore the energy applied to the heating element can be kept constant. The print density can be maintained constant.

Embodiment A first embodiment of the present invention will be described with reference to FIGS. 1 to 3. Components that are the same as those described in FIGS. 6 to 8 are designated by the same reference numerals, and description thereof will be omitted. Voltage dividing resistors 27 and 28 are connected in series to the power supply 7, and the midpoint of these voltage dividing resistors 27 and 28 and the thermistor 22 are connected to an analog switch 29. This analog switch 29
is connected to the input side of CP tJI via the A/D converter 3o, and is connected to the input side of CP tJI via the output port 31.
The contacts are switched by a control signal i'f output from the control signal i'f. That is, the analog switch 29 selectively passes the voltage data of the power supply 7 and the voltage data of the thermistor 22, and the Δ/D converter 30 has a voltage detection means for detecting the voltage of the power supply 7 and a voltage detection means for detecting the voltage of the heating element 18. It has two functions: a temperature detection means for detecting the nearby temperature (voltage of the thermistor 22).

In such a configuration, the operation will be explained with reference to the timing chart shown in FIG. 2 and the flow chart shown in FIG. 3. First, the average resistance value of the heating element 18 is the switch 2
It is set by operating 3. This average resistance value is read into the CPUI. Also, the printing cycle T of the l line
The start is 1 when the interrupt of the first counter I5 occurs.
11, the printing cycle T is constant. Here, to show the operation from time A to time B shown in the timing chart of FIG. 7, the A/D converter 30 is
Temperature data from the output of the thermistor 22, that is, near the heating element 18, is read into the CPUI, and the print data of the next line is transferred to the shift register 19 of the thermal head 17. Subsequently, when an interrupt of the first counter 15 occurs, the pulse motor 9 is driven by one line, and the printing paper is fed. Subsequently, the second counter 16 is set to the power supply time to the heating element 18, the analog switch 29 is switched to the power supply 7 side by the control signal from CPtJl, and the power supply is turned on by the ECN 13 = O signal from the CPUI. A voltage from 7 is applied to heating element 18 . The energization time L1 at this time is the shortest possible time considering voltage fluctuations and temperature changes when driving the heating element 18 with the average resistance value specified by the switch 23, and the energization time is corrected later. be. In other words, Δ/
The output from the D converter 30, that is, the voltage V of the power supply 7 during discharging is read, and the heating element The energy E applied to 18 is R
Obtained from the OM2 table.

The optimum energization time for the heating element 18 is calculated using the formula ``t = RE/V'', and the difference □ between this energization time t and the provisional energization time L1 previously set in the second counter 16 is calculated. Then, when an interrupt of the second counter 16 occurs one hour after setting the second counter 16, the L value is set to the second counter 16.
y is set, and after 1 hour the second counter y is set.
When '6 interrupt occurs, ENB=1 from CPUI.
This signal cuts off the power supply to the heating element 18 from the power supply 7, and then the analog switch 29 is switched to the thermistor 22 side by a control signal from the CPUI. The above is the printing cycle T of one line printing in the timing chart in FIG. 2, and this cycle T is repeated as long as the print command signal continues.

Incidentally, since the thermistor 22 reacts slowly to temperature changes, the temperature reading may not be carried out every time one line is printed, but may be carried out every time several lines are printed. Further, a large number of heating elements 18 arranged on a line may be divided into a plurality of blocks and energized.

In this case, if the number of divided blocks is n, then by repeating the operation of the flowchart shown in Fig. 3 n times, l
The line is printed. However, in this case, it is sufficient to drive the pulse motor 9 once every n times to feed the printing paper one line. Further, although the printing cycle 'l' was set constant, it may be changed depending on the time Lt+t.

Next, a second embodiment of the present invention will be described with reference to the timing chart shown in FIG. 4 and the flow chart shown in FIG. 5. In this embodiment, the average resistance value of the heating element 18 currently being printed and the temperature near this heating element 18 are determined. ,hX7
Based on the voltage ■, the heating element 18 for printing the next line
The purpose of this embodiment is to calculate the time for the passage 1 to 1, and the other components are the same as those of the previous embodiment, so a description thereof will be omitted. Note that the flowchart shown in FIG. 5 is from point A to point B shown in FIG.
This is about the period leading up to the point in time. Now, when an interrupt of the first counter 15 occurs, the pulse motor 9 is driven by one line, and the printing paper is fed. Subsequently, the time period for energizing the heating element 18 determined during printing of the previous line is set in the second counter 16.

The operation for determining this energization time will be described later. Next, cp
The analog switch 29 is switched to the power supply 7 side by the control signal of ul, and the voltage is applied from the power supply 7 to the heating element 48 by the signal ENB=O from the CPUI, and is transferred to the shift register 19 of the thermal head 17 during printing of the previous line. Printing is performed using the print data. Next, the CPU
When the data of the voltage V of the power supply 7 is read from the A/D converter 30 by I, and the time set in the second counter 16 has elapsed, an interrupt of the second counter 16 occurs, and a signal is output from CP[Jl. ENB=1 is output, and the power supply from the power source 7 to the heating element 18 is cut off. Next, the analog switch 29 is switched to the thermistor 22 side by the CPU control signal, and the CPU reads the output of the thermistor 22 (temperature near the heating element 18) from the A/D converter 30, and prints the next line. Then, the print data for printing the next line is transferred to the shift register 19 of the thermal head 17. This ends the printing period T of - times, but this printing period T is repeated by the printing command.

In this way, when printing the current line, the energization time for printing the next line is set, so the heating element 18 is actually
What is the optimal power supply based on the voltage of power supply 7 when driving? 1 hour can be set. In addition, when printing a barcode, the same print data continues over many lines, so the energization time calculated during printing of the current line is applied as the ttn when energizing the next line without the slightest error. Therefore, it is an extremely effective method.

Effects of the Invention Since the present invention is configured as described above, even if the voltage of the power supply changes, it is possible to calculate the optimum energization time to the heating element by taking into account the change in the voltage input from the voltage detection means. Therefore, the energy applied to the heating element can be kept constant, the printing density can be made constant, and an inexpensive power source with large voltage fluctuations such as a small capacity power source or battery can be used. Furthermore, by calculating the current supply time to the heating element for printing the next line based on the average resistance value of the heating element currently being printed, the temperature near this heating element, and the voltage of the power supply, The optimum energization time can be set based on the voltage of the power supply when driving.
When printing barcodes, the same print data continues over many lines, so the energization time calculated during printing of the current line can be applied as the energization time of the next line without the slightest error. It has the effect of

[Brief explanation of drawings]

1 to 3 show a first embodiment of the present invention, in which FIG. 1 is an electronic circuit diagram, FIG. 2 is a timing chart, FIG. 3 is a flowchart, and FIGS. 4 and 5 are This shows a second embodiment of the present invention; FIG. 4 is a timing chart, FIG. 5 is a flowchart, and FIGS. 6 to 8 are conventional examples. FIG. 6 is an electronic circuit diagram, and FIG. The figure is a timing chart, and FIG. 8 is a flowchart. ■...Arithmetic unit, 7...Power source, 8...Head drive circuit, 14...Average resistance value detection means, 17...Thermal head, 18...Heating element, 22...Temperature measurement Motoko, 3
0...Temperature detection means/voltage detection means

Claims (1)

[Scope of Claims] 1. A power supply to which a heating element of a thermal head is connected, a temperature detection means including a temperature measuring element located near the heating element, a voltage detection means connected to the power supply, and a temperature detection means connected to the power supply; The detection means and the voltage detection means are connected to the input side, and the head drive circuit connected to the power supply is connected to the output side. A thermal head energization control circuit, characterized in that a temperature and a voltage of the power source detected by the voltage detection means are input to the calculation section to calculate the energization time to the heating element. 2. A power supply connected to the heating element of the thermal head, a resistance value detection means connected to the heating element, a temperature detection means including a temperature measuring element located near the heating element, and a temperature detection means connected to the power supply. The calculation unit includes a voltage detecting means, the resistance value detecting means, the temperature detecting means, and the voltage detecting means connected to an input side, and a head drive circuit connected to the power source connected to an output side, The average resistance value of the heating element detected by the resistance value detection means, the temperature near the heating element detected by the temperature detection means, and the voltage of the power supply detected by the voltage detection means are sent to the calculation unit. A thermal head energization control circuit, characterized in that the circuit calculates the normal time for the heating element by inputting the input power. 3. The thermal printer according to claim 1 or 2, wherein the time for energizing the heating element for printing the next line is calculated based on at least the temperature near the heating element and the voltage of the power supply. Head energization control circuit.