JPS6327272A - Thermal printer - Google Patents

Abstract

PURPOSE:To prevent the irregularity of printing density due to the exhausion of a battery, by changing a printing compensation current according to the voltage drop of a battery power source and compensating a printing pulse width according to said printing compensation current. CONSTITUTION: In order to compensate the lowering in the voltage V1 of a battery exhausted, a current supply circuit is equipped with a current supply source 13 operated on the basis of the difference between battery voltage V1 and the output V2 of a voltage regulator. The current supply source 13 comprises a series circuit of a non- linear element (e.g., constant voltage diode ZD) and a resistor R3 and, when the voltage V1 of the battery is low and the constant voltage diode ZD is held to an ON-state, the current determined by the resistor R3 flows in the base of a transistor Q and a current charging a condenser C is made large. Therefore, a printing pulse width becomes short and a thermal head 4 is driven so as to consume constant power. Since the inverse characteristic of the constant voltage diode ZD is used at a relatively smooth part, control can be performed so as not to generate sudden compensation. However, since a compensation current changes non-linearily, said current has a compensation width sufficient to compensate the voltage of the battery lowered by exhausion.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a thermal printing device, and more particularly to a thermal printing device that improves fluctuations in thermal printing density due to changes in battery voltage in a portable electronic blood pressure monitor or the like.

[Prior Art and Problems Therewith] Thermal printing devices are popular in portable electronic devices because they are small and have good printing quality. However, since the print density changes depending on the power consumption of the thermal head, for example, if the power supply battery is exhausted, the print density will vary and the print will become unclear. One of the causes of variations in print density is fluctuations in the voltage of the exhausted battery. Particularly when driving segments of the thermal head, large load fluctuations occur, causing the battery voltage to drop over time. Another cause is that the concentration changes due to the normal temperature rise of the thermal head.

Conventionally, this problem has been solved using a configuration as shown in FIG. In the figure, 1 is a power supply battery that generates battery voltage v1, 2 is a constant voltage regulator (VR) including a booster circuit that forms a constant voltage v1 from battery voltage v1, 3 is a thermal head drive control circuit, and 4 is a thermal head drive control circuit. 5 is a tacho generator for detecting the movement of a thermal head carriage (not shown); 6 is an amplifier (AMP) for tacho signals; and 7 is a microprocessor (C) for main control of the thermal printing device.
PtJ), 8 is a latch that holds thermal print data,
9 is a drive circuit that thermally drives the thermal head; 11, 12;
constitutes a one-shot circuit 10 that generates a thermal printing pulse. It should be noted that the latch 8 outputs latch data to its output terminal 0 while the thermal printing pulse applied to its probe terminals S1 to S is logic "1".

A current supply circuit consisting of a transistor Q determines the thermal printing pulse width of the one-shot circuit 10. At the same time, it is intended to compensate for thermal power caused by fluctuations in battery voltage (1). That is, the battery voltage (1) drives the base of the current supply transistor Q via the bias resistor R1 and the variable resistor VR, so if the battery voltage V1 temporarily decreases due to load fluctuations caused by driving the Herad carriage, etc., the voltage is applied to the capacitor C. The charging current becomes smaller, thereby increasing the thermal printing pulse width of the one-shot circuit 10 and compensating the thermal power to remain constant. Further, as the battery voltage V1 increases, the charging current to the capacitor C increases, and accordingly, the thermal printing pulse width of the one-shot circuit 10 becomes shorter, and the thermal power is compensated to be constant.

Furthermore, in order to reduce the influence of the outside temperature on the print density and to prevent thermal deterioration of the thermal head, the print τ ambient temperature is detected by the current supply transistor Q provided.

That is, as the temperature of transistor Q increases, the current amplification factor H
Since fe becomes larger, the charging current to capacitor C becomes weaker, and the printing pulse width becomes shorter. Furthermore, as the temperature of the transistor Q decreases, the current amplification factor Hfe decreases, so the charging current to the capacitor C decreases, and the thermal printing pulse width increases. In this way, changes in thermal print density due to temperature are compensated for.

In this way, in the past, changes in thermal print density due to voltage fluctuations and temperature during dot driving of a thermal head have been dealt with. However, if the battery voltage fluctuates greatly and you intend to use it down to a low battery voltage, if you take this compensation range too far, the difference between a new battery and a depleted battery will be slightly different, and the battery will become depleted. A dark state occurs when the voltage drops. Therefore, in the past, there was a drawback that the print density changed depending on the state of battery consumption.

[Purpose of the Invention] The present invention solves the problems of the prior art described above, and its purpose is to provide a thermal printing device that eliminates variations in print density due to battery consumption, and more specifically, to provide a thermal printing device that eliminates variations in printing density due to battery consumption. An object of the present invention is to provide a portable electronic blood pressure monitor with the following features.

[Summary of the invention] This object is achieved according to the invention by a thermal printing device as follows. That is, this thermal printing device
A thermal printing device that adjusts printing density by changing a printing pulse width, the thermal printing device comprising: a thermal head loaded on a battery power source; a current compensation circuit that changes a printing compensation current according to a voltage drop of the battery power source; and the printing compensation current. and a pulse generation circuit for compensating the printing pulse width according to the printing pulse width.

According to one aspect of the invention, the current compensation circuit includes a series circuit of a resistor and a nonlinear element connected to a battery power source.

[Detailed description of the invention and operation instructions] Examples of the present invention will be described in detail below.

1, 2(a) and 2(b) relate to detailed explanation of the present invention, FIG. 1 is a block diagram of a thermal printing device according to an embodiment, and FIG. 2(a) is a block diagram of a thermal printing device according to an embodiment. A timing chart showing each waveform, and FIG. 2(b) is a diagram showing the one voltage current characteristic of the constant voltage diode ZD. In FIG. 1, the same components as those in FIG. 3 are given the same numbers and their explanations will be omitted.

In FIGS. 1 and 2(a), the tacho generator 5 detects the movement of the thermal carriage pixel by pixel and outputs a detection signal. The AMP 6 amplifies this signal, binarizes it, and outputs a carriage signal ■. Carriage signal ■
The level is inverted by the NOR gate 11 and the carriage signal ■
become.

Furthermore, the carriage signal (2) is differentiated by the capacitor C and becomes a negative spike signal (2). The rise curve of the spike signal (2) changes depending on the current of the current supply circuit consisting of the transistor Q. That is, when the supplied current is large, it rises steeply, and when it is small, it rises slowly. NOR Kate 12
In this case, the level of the spike signal (2) is binarized using its own gate threshold to form a thermal printing pulse signal (2).

In addition, the CPU 7 outputs a reset signal ■ after a predetermined period of time in synchronization with the thermal printing pulse signal ■, and the diode D
The capacitor C is discharged in the opposite direction through the .

This is to make the negative level of the spike signal (2) deep and to obtain a sufficient range of printing pulse width.

As described above, the pulse width of the print pulse signal (2) in the embodiment also depends on the current supplied from the current supply circuit. However, the bias circuit including the variable resistor VR operates at Vl. Therefore, it follows fluctuations in battery voltage depending on the number of printed dots operated by the thermal head. On the other hand, in order to compensate for the drop in the voltage V1 of the exhausted battery, the current supply circuit of the embodiment includes a current supply source 13 that operates based on the difference between the battery voltage V1 and the output V2 of the voltage regulator. The current supply source 13 consists of a series circuit of a nonlinear element (for example, a constant voltage diode ZD) and a resistor R3,
When the battery voltage V1 is low and the constant voltage diode ZD is in the ON state, a current determined by the resistor R3 flows into the base of the transistor Q, increasing the charging current to the capacitor C. Therefore, the printing pulse width becomes short, and the thermal head 4 is driven to consume constant power.

As shown in FIG. 2(b), the inverse characteristic of the constant voltage diode ZD uses a relatively smooth portion. Therefore, it is possible to control so that sudden compensation does not occur. However, unlike the conventional type, the compensation current changes non-linearly, so it has a compensation width sufficient to compensate for the battery voltage that has decreased due to consumption. That is, in this embodiment, the current supply source 13 is set so as not to suppress the pulse width when the battery voltage is sufficient. Therefore, when the battery voltage V1 eventually becomes low and the voltage regulator diode ZD is turned on, the current from ZD flows into the heath of the transistor Q, so the charging current to the capacitor C increases, and finally approaches the power supplied to the head set by the variable resistor VR when the battery voltage is high.

Further, the printing ambient temperature is detected by the current supply transistor Q and the constant voltage diode ZD. That is, as the temperature of the transistor Q increases, the current amplification factor Hfe increases, so the charging current to the capacitor C increases and the print pulse width becomes shorter. Moreover, since the ON%E voltage of the constant voltage diode ZD becomes smaller, the compensation is applied synergistically. Also, when the temperature of transistor Q decreases, the current amplification factor H
Since fe becomes smaller, the charging current to the capacitor C becomes smaller, and the thermal printing pulse width becomes longer. In this case as well, since the ON voltage of the constant voltage diode ZD increases, the compensation is applied synergistically. In this way, changes in thermal print density due to temperature can be compensated for by 1-min.

[Effects of the Invention] As described above, according to the present invention, changes in print density due to fluctuations in battery voltage due to battery consumption can be reduced. Also, changes in print density due to the influence of outside temperature can be reduced. Therefore,
For example, it is possible to print out clearly the measured values and graphed data of a portable device such as an electronic blood pressure monitor, thereby eliminating the unreadable state.

Further, since the concentration can be sufficiently compensated for from a high battery voltage to a low battery voltage, the usage time of the battery is extended.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a thermal printing device according to an embodiment of the present invention, Fig. 2(a) is a timing chart showing waveforms equivalent to Fig. 1, and Fig. 2(b) is a diagram of a voltage regulator diode. FIG. 3 is a block diagram of a conventional thermal printing device. In the figure, 1... power supply battery, 2... voltage regulator (
VR), 3... Thermal head drive control circuit, 4.
... Thermal head, 5... Tacho generator, 6...
・Amplifier (AMP), 7... Microprocessor (C
PU), 8...Latch, 9...Drive circuit, 1o...
・One-shot circuit, 11.12...NOR gate. Patent applicant: Terumo Corporation No. 2rM (b)

Claims (2)

[Claims] (1) In a thermal printing device that adjusts printing density by changing the printing pulse width, a thermal head loaded with a battery power source, a current compensation circuit that changes a printing compensation current according to a voltage drop of the battery power source, and the printing A thermal printing device comprising: a pulse generation circuit that compensates a printing pulse width according to a compensation current. (2) The thermal printing device according to claim 1, wherein the current compensation circuit includes a series circuit of a resistor and a nonlinear element connected to a battery power source.