JPH0351162Y2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a battery-driven thermal recording printing device that automatically checks the battery voltage during printing and adjusts the pulse width of the drive current applied to the print head according to the battery voltage. It is made to be variable.

Generally, a print head in a thermal recording type printing device basically performs printing by utilizing heat generated by passing a current through an electric resistance. The driving conditions for this print head vary depending on its heat capacity or heat dissipation resistance, but generally the first
It becomes a curve as shown in the figure and is not linear. As is clear from this figure, in order to keep the drive current pulse width constant, the power supply voltage must be constant. However, when using batteries as a power source,
The battery voltage gradually decreases over time of use. Therefore, the condition that the power supply voltage must be constant cannot be satisfied.

Conventional battery-powered printing devices either do not compensate for a drop in power supply voltage at all, or adopt a system in which a drop in power supply voltage is anticipated in advance and stabilized at a low voltage. However, with no compensation for voltage drop, the print is dark when the battery is new, but as the battery wears down and the voltage drops, the print becomes lighter and becomes uneven. In addition, in the case where the voltage drop is anticipated in advance, the number of batteries used is large, and the higher the voltage, the more energy is wasted, which is uneconomical, and the overall size of the device becomes large. Another possibility is to perform constant voltage control within the circuit, but there is a problem in that a power supply that allows for voltage drops must be used, and a considerable amount of energy is consumed for voltage control.

The present invention was developed to solve the above-mentioned drawbacks and problems. During printing, the battery voltage is checked and the drive current pulse width applied to the print head is changed according to the checked battery voltage. This is how it was done. With this configuration, it is possible to print with a constant quality from the time the battery starts being used until the end of its life, and there is no energy wastage, so the number of batteries is kept to a minimum, and the overall shape and weight are also reduced. This can be done to a minimum.

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

In Fig. 2, 1 indicates a numeric keypad, a character key,
A keyboard consisting of function keys, etc.
This keyboard 1 is coupled to a CPU (central control unit) 2 that inputs and outputs various control signals for printing. This CPU 2 also includes a RAM (random access memory) 3 that inputs and outputs input data, etc., and a RAM (random access memory) 3 that outputs program data.
a ROM (read only memory) 4; a mechanical drive section 6 provided via a mechanical drive circuit 5;
Thermal printing heads 8 provided via head drive circuits 7 are respectively coupled. The RAM 3 or ROM 4 is provided with a table of drive current pulse widths predetermined in multiple stages. Further, 9 is a battery power source for driving the entire printing apparatus.

Next, 10 is a voltage check circuit added according to the present invention. This voltage check circuit 10
consists of a voltage detection section 14 consisting of a resistor 11, a capacitor 12 and a transistor 13, a reference voltage setting section 19 consisting of a transistor 15, a Zener diode 16, a protection resistor 24 and voltage dividing resistors 17 and 18, and a voltage comparison circuit 20. has been done.
The voltage Vr at the connection point between the voltage dividing resistors 17 and 18 is applied to the +input side of the voltage comparison circuit 20, and the voltage Vc at the connection point between the resistor 11 and the capacitor 12 is applied to the -input side, and the output The side is coupled to a timer circuit 21 within the CPU 2. The base of the transistor 13 is coupled to a voltage check trigger pulse signal terminal 22 of the CPU 2, and the base of the transistor 15 is coupled to a voltage check time drive pulse signal terminal 23. As the voltage check trigger pulse, for example, a paper feed signal, a line feed signal, a head return signal, a pulse signal when the power is turned on, etc., which are generated during a printing interruption period, are used. The voltage check time driving pulse is a pulse signal that falls in synchronization with the voltage check trigger pulse and rises a little later than the rise of the voltage comparison circuit 20.

Next, the operation of the printing apparatus according to the present invention will be explained with reference to the waveform diagram of FIG. 3 and the flowchart of FIG. 4.

Figure 3a is synchronized with the paper feed signal that is output when one line of printing is finished, for example, at _t1 during the printing interruption period.
A trigger pulse signal as shown in is output from the terminal 22 of the CPU 2. This trigger pulse signal turns on the transistor 13, discharges the charge in the capacitor 12, and the voltage Vc becomes zero. At the same time, the signal shown in Figure 3b from the terminal 23 of the CPU 2 falls, the transistor 15 turns on, and the resistor 1
A reference voltage Vr as shown in FIG. When the reference voltage Vr rises to a predetermined constant value at _t2 and the trigger pulse signal disappears, the transistor 13 is turned off, so the resistor 11
Charging of the capacitor 12 is started via the capacitor 12. When the battery 9 is new, the voltage is sufficiently high, so the charging characteristics rapidly increase as indicated by the solid line Vc. Furthermore, as the battery 9 ages, the voltage also decreases, so the charging characteristics gradually increase as indicated by the dotted line Vc. At the same time as the trigger pulse falls at the time _t2 , the timer circuit 21 in the CPU 2 is activated and starts counting the number of pulses. When the battery 9 is new, it reaches t ₃ o'clock, and when the battery 9 is old, it reaches t ₄ o'clock, and the charging voltage Vc of the capacitor 12 reaches the reference voltage Vr. The output is output as shown below, and the timer circuit 21 in the CPU 2 is stopped.
Data N corresponding to the number of pulses is output, and this data N is sent to the CPU 2. Data N is compared with division values n ₁ , n _{2 .}
T ₀ , T ₁ , ... corresponding to n ₁ , n ₁ <N≦n ₂ , _no <N
Output either Tn. Then, the CPU 2 outputs drive pulses P ₀ , P ₁ . . . corresponding to T ₀ , T ₁ , . . . Tn.
Pn is output and the thermal printing head 8 is driven for the time corresponding to the pulse width to print.

After the above t ₃ or t ₄ , the voltage at the terminal 23 rises with a slight time delay, and therefore the reference voltage
Vr quickly drops to zero.

In the embodiment shown in FIG. 2, the reference voltage setting section 1
9 uses the transistor 15 to generate the reference voltage Vr for the voltage check time, but
If the current consumption is small, this transistor 1
5 may be omitted and connected directly to the battery 9.

As mentioned above, the present invention checks the battery voltage during printing in a battery voltage-driven printing device, and
The pulse width of the head drive current is controlled according to the voltage. Therefore, when the voltage is high, the print head is driven with a small pulse width, and when the voltage is low, the print head is driven with a large pulse width, and the battery can print with a constant quality from the time it is used until the end of its life. In addition, since there is no wasted energy, only the minimum number of batteries are required, and there are no running costs.
Moreover, the weight can be minimized and the size can be reduced. moreover,
It can be used until the life of the battery. If the voltage check circuit is checked using the printing interruption period, the power consumption for checking is small, and the control circuit for printing control can be shared, making the circuit configuration simple.

[Brief explanation of drawings]

FIG. 1 is a characteristic diagram showing the relationship between the drive current applied to the print head and the drive current pulse width, FIG. 2 is an electric circuit diagram showing an embodiment of the printing device according to the present invention, and FIG. Output waveform diagram of each part in
Figure 4 is a flowchart. 1...Keyboard, 2...CPU, 3...
RAM, 4...ROM, 8...Print head, 9...
... battery, 10 ... voltage check circuit, 14 ... voltage detection section, 19 ... reference voltage setting section, 20 ... voltage comparison circuit, 21 ... timer circuit.

Claims (1)

[Scope of claim for utility model registration] (1) Printing data entered from the keyboard,
In a battery-powered thermal recording type printing device, processing is performed by a control circuit consisting of a CPU, RAM, and ROM, and the print head is operated and printed by a drive current pulse signal from this control circuit. a voltage detection means for detecting a charging voltage of a capacitor of a time constant circuit coupled to a reference voltage setting section for generating a reference voltage based on a trigger pulse signal from a control circuit, and comparing and outputting the charging voltage and the reference voltage. Consists of a voltage comparison circuit,
A voltage check circuit detects the time taken for the charging voltage to reach a reference voltage from 0 using a timer circuit in the CPU, and the output of the timer circuit corresponds to a print head drive pulse width predetermined in multiple stages. 1. A printing device comprising a table, wherein a pulse width corresponding to an output of a timer circuit is selected from the table, and a drive current pulse signal is output to a head drive circuit. (2) The printing device according to claim 1, wherein the voltage check circuit is driven by a pulse signal generated during a printing interruption period such as a paper feed signal, a line feed signal, or a power-on signal from a control circuit. .