JPH0548185B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a thermal print head drive that controls the density of printing and the size of raw dots regardless of each speed mode in a thermal printer having various spacing speed modes. It is about the method.

(Background Art) A control block diagram of a conventional thermal printer is shown in FIG. 1 is the control unit, mainly CPU, I/
It consists of an O port, timer, etc. 2 is
A thermal head drive circuit supplies a drive voltage (power supply voltage) from a control section 1 to a thermal head 3 with a time width corresponding to a print signal (print time). 4
is a motor drive circuit that supplies a drive current to the motor 5 in response to a control signal from the control section 1.
The motor 5 has a built-in speed detector, converts a voltage corresponding to the rotational speed into pulses through an analog-to-digital converter (hereinafter referred to as an A/D converter), and feeds it back to the control section 1. The feedback signal is used for constant speed control of the motor and as a print timing for the head 3. 7 is a logic power supply, and its output V _L is mainly supplied to the control section 1 . 8 is a power source, whose output V _P is sent to the thermal head 3 via the thermal head drive circuit 2, and to the motor drive circuit 4.
It is supplied to the motor 5 via. The operation of the thermal printer will be explained using FIG. 1. The control unit 1 counts the interval of pulses fed back from the motor 5 via the A/D converter 6 using a timer or the like included in the control unit 1, and makes sure that the rotational speed of the motor 5, that is, the spacing speed, is at the target speed. A control signal is sent to the motor drive circuit 4 so that the motor rotates at a constant speed. In response to the control signal, the motor drive circuit 4 outputs a drive voltage, a drive signal for the motor 5, etc. to the motor 5 to rotate the motor 5. The motor 5 outputs feedback pulses to the control unit 1 via the A/D converter 6 as it rotates. Regarding motor control, this operation is repeated below. When changing the spacing speed, the control section 1 must change the parameter (feedback pulse interval) used in the calculation in the part that calculates the control signal output to the motor drive circuit 4 from the feedback pulse. This is done by Next, driving of the thermal head 3 will be explained. As mentioned above, the printing timing is determined by motor 5.
A feedback pulse inputted to the control unit 1 via the A/D converter 6 is used. Control part 1
By inputting the feedback pulse, a print signal (printing time) at the position of the feedback pulse is given to the thermal head drive circuit 2, and the circuit 2 supplies head heating power to the thermal head 3. Printing is performed by coloring thermal paper or by thermally transferring ink. Then, the next feedback pulse is inputted again, and this operation is repeated thereafter.

Here, the printing mechanism of the thermal head 3 will be explained. Thermal head 3 is the second one when written as an equivalent circuit.
As shown in the figure, it consists of a large number of resistors 17 (resistance value R ohms). By applying a driving voltage as shown in FIG. 3 to the resistor 17, P=
The electric power V _P ² /R·T is consumed, and with the Joule heat generated in the resistor 17 by this electric power, printing is performed on thermal paper or plain paper via a thermal transfer ribbon.

The density of the raw dots of characters printed on thermal paper or plain paper via a thermal transfer ribbon is determined by the temperature of the thermal print head. Therefore, in order to print at the same density, the same power must be supplied to the thermal head 3. That is, as shown in FIG. 1, when the output of the power source 8 for driving the thermal head is the voltage V _P , and the power to be applied is P, the driving time T is T.
= P·R/V _P ² , and if this time T is kept constant, it is possible to print at the same density.

In the conventional thermal head driving method, as described above, the driving time T is kept constant (excluding the correction of the driving time T to correct the temperature rise when repeatedly printing the same dot), and printing is performed at the same density. It has the following drawbacks:

First, there is a demand for printing even when the space motor is accelerating and decelerating to eliminate wasted time. Also, since the dot density differs depending on the font or design, control is performed such that low dot density is printed at high speed, and high dot density is printed at low speed, thereby uniformizing the load on the power supply. It is required to do so. This method can print characters at a fairly high speed even when using a relatively small-capacity power supply, and has the advantage of not burning out the power supply even if high dot density is applied continuously, so it is compact and inexpensive. This is an effective method for printers.

However, when printing using the conventional method described above by changing the printing speed, that is, the spacing speed,
Since the driving time T is constant, as shown in FIG. 4, the distance traveled by the thermal print head with the amount of heat required for printing varies, and the length of color development varies. For example, if you run at 60 CPS (characters per second)
Compared to 30CPS, the raw point length is approximately twice as long, and conversely, when running at 15CPS, the raw point length is approximately half that of 30CPS. In Figure 4, one character is
12-dot configuration, 10 characters/inch, printing interval of 1 dot is 1/60 inch. Since the length of the raw dots printed in this manner increases or decreases depending on the spacing speed, there is a drawback that the same character or design is printed with different line widths, resulting in irregularities.

(Problems to be solved by the invention) The purpose of the present invention is to solve these drawbacks.
The head drive power supply voltage and drive time are controlled by the spacing speed while the power supplied to the head is constant, and the size of the raw points is made variable.This will be described in detail below.

(Structure and operation of the invention) FIG. 5 is a block diagram of an embodiment of the invention, in which the control unit 1 is read out in response to the spacing speed and corresponds to a value proportional to the square root of the spacing speed. The head drive voltage table 101 outputs a predetermined head drive voltage digital control signal, is read out in response to the spacing speed, and outputs a predetermined count value in inverse proportion to the spacing degree. It is provided with a head drive time table 102 and an internal timer 103 that counts time based on the count value of the head drive time table. 9 is a D/A converter that converts the head drive voltage control signal, which is changed depending on the spacing speed, sent from the control unit 1 into an analog signal;
Reference numeral 10 denotes a head voltage generating circuit which boosts or lowers the power supply voltage V _P in accordance with the head drive voltage analog control signal from 9 to generate a head drive voltage. FIG. 6 shows an embodiment of the head voltage generating circuit 10, which is a step-down type. 11 in Figure 6
is a transistor, 12 is a resistor, 13 is a diode, 14 is an inductance, 15 is a capacitor,
16 is an error amplifier, sample hold, oscillator,
This is a switching regulator circuit composed of an integrator, a comparator, etc. FIG. 7 shows an example of the operating waveforms of this circuit. Further, FIG. 8 is an operation flowchart of the control section 1 for explaining this embodiment.

The operation of this circuit will be explained with reference to FIGS. 7 and 8. 60cps as spacing speed,
If you have three speed modes of 30cps and 15cps,
(Here, CPS is CHARACTER PER SECOND
Set the space speed in [characters/second]. ) In other words, in the case of a relatively normal number of printing dots (normal character printing),
If you want to change the printing speed depending on whether the print speed is slightly large (graphic printing) or very large (hard copy, etc.), change the standard (60 cps) drive voltage to the voltage.
Assume that V _P is time T. The control unit 1 controls the spacing speed (printing speed) before printing.
(In the example shown in FIG. 8, the square root of the spacing speed is stored in a table in advance and read out in correspondence with the preset spacing speed before printing.) Head drive voltage It is output to the D/A converter 9 as a control signal. The control signal is converted into an analog control signal by the D/A converter 9 and output to the head voltage generation circuit 10. In the head voltage generation circuit, the analog control signal is compared with the head voltage described later by a switching regulator circuit 16, and the transistor 11 is switched on and off so that the head voltage reaches the voltage level specified by the analog control signal. Generates voltage.

In the example shown in Figure 7, the head voltage is V _P when the speed is 60 cps, and the speed is 1/2 when the speed is 30 cps.
V _P /√2, since the speed is 1/4 in the case of 15 cps
V _P /2. In this way, the supplied power P ₆₀ ,
The control of the space motor in which P ₃₀ and P ₁₅ are constant and the size of the raw point is also constant is the same as in the prior art. Printing is controlled by A/D from motor 5.
By inputting the feedback pulse to the control unit 1 via the converter 6, the print signal at the feedback pulse position is determined as a time inversely proportional to the spacing speed, that is, the time required for the same spacing distance. Thermal head drive circuit 2
Send to. In the example in Figure 7, when the speed is 60cps, the time is T, and since the speed of 30cps is 1/2, the time is 2T, which is 15cps.
In the case of , the speed is 1/4, so the time is 4T.
In the flowchart of FIG. 8, a timer inside the control unit is used to perform this operation, and the time is determined by using a table. In the thermal head driving circuit 2, the head voltage generated by the head voltage generating circuit is supplied to the thermal head 3 for the above-mentioned period of time to perform printing. Then, the next feedback pulse is inputted again, and this operation is repeated thereafter.

FIG. 9 is a diagram showing the relationship between printing speed, drive voltage, and drive time. In the solid lines in a and b of the same figure, which indicate this embodiment, the drive voltage is greatly changed with respect to the speed change, and the drive time is also changed relatively largely. Note that in the dashed line representing the prior art, the drive voltage is constant and does not change depending on the speed.

(Effects of the Invention) As explained above, in this embodiment, the head drive voltage and head drive time are read out from the table so that the power supplied to the thermal head is constant with respect to the spacing speed. In addition, since the head drive voltage and drive time are controlled as a function of speed by the spacing speed, and the power supplied to the thermal head is kept constant, the size of the printed raw dots can be adjusted by the spacing speed. In addition, when the drive time is shortened, the drive voltage is increased, so there is no possibility that the time until color development is not reached due to the short drive time, and a constant print density can be obtained. Furthermore, since the energy applied to the print head (supplied power=V _P ² /R·T) is always constant, the power supply can be downsized. Therefore, even if the spacing speed is made variable based on the number of printing raw points due to restrictions such as power supply capacity, the printed characters can be kept constant regardless of the spacing speed. That is, the thermal print head drive device according to the present invention has the advantage that high print quality can be achieved even with a minimum power supply capacity in order to reduce the size and power consumption of printers in the future.

In the present invention, the driving voltage and driving time of the thermal head are controlled by the spacing speed so that the power supplied to the thermal head is constant, and the size of the print element is kept constant. This has the effect of keeping the line width constant even if the line width is changed.

[Brief explanation of the drawing]

Figure 1 is a control block diagram of a conventional thermal printer, Figure 2 is an equivalent circuit of a thermal print head,
3 is a thermal print head drive waveform, FIG. 4 is a time chart of a conventional thermal print head drive, FIG. 5 is a control block diagram of a thermal printer according to the present invention, and FIG. 6 is a head voltage generation circuit according to the present invention. One embodiment, FIG. 7 is a time chart for driving the thermal print head in the present invention, and FIG.
The figure shows the operation flow of the control section in the present invention, and FIG. 9 is a diagram showing the relationship between printing speed, drive voltage, and drive time. DESCRIPTION OF SYMBOLS 1...Control part, 2...Thermal head drive circuit, 3
...Thermal print head, 4. Space motor drive circuit, 5. Space motor, 6. Analog-to-digital converter, 7. Logic power supply, 8. Power supply, 9. Digital-to-analog converter, 10. Head voltage generation. Circuit, 11...Transistor, 12...
Resistor, 13...Diode, 14...Smoothing choke coil, 15...Smoothing capacitor, 16...Switching regulator circuit, 17...Heating resistor of thermal printing head, 101...Head drive voltage table, 102...Head drive time table , 103
...internal timer.

Claims (1)

[Claims] 1. In a thermal printing head driving device that prints a dot pattern by energizing the heating elements of the thermal printing head while spacing the paper continuously, , a head drive voltage table storing a predetermined head drive voltage digital control signal, a head drive time table storing a predetermined count value so as to be inversely proportional to the spacing speed, and a head drive time table storing a predetermined count value inversely proportional to the spacing speed; a control unit including an internal timer that counts time based on the read count value; and a control unit that uses a head drive voltage digital control signal read from the head drive voltage table in accordance with a preset spacing speed to adjust the spacing speed. a digital-to-analog converter for converting a head drive voltage analog control signal proportional to the square root; a transistor; and a transistor for comparing the head drive voltage analog control signal from the digital-to-analog converter with an output head voltage to switch the transistor. a switching regulator for controlling the head voltage so as to be proportional to the square root of the spacing speed; a thermal head drive circuit that applies a head voltage from the head voltage generating circuit to the thermal print head for a time inversely proportional to the spacing degree counted by the internal timer to keep the power supplied to the thermal print head constant; A thermal printing head drive device comprising: .