JP2000168119A - Printer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain constant printing quality irrespective of lowering of an output voltage of a battery which may occur when an internal resistance is increased along with the deterioration due to repetition of charging and discharging or when a charged quantity is reduced along the using of a portable printer. SOLUTION: An internal resistance of a battery is obtained (step S2) based on an electromotive force of the battery which is obtained by measuring a power source voltage (step S1) in a non-loading condition that a thermal head is not energized, a resistance value of few of heating elements provided on the thermal head and a power source voltage which is measured (step S1) in a loading condition that the few of the heating elements are energized. A voltage applying time period to the thermal head is determined (step S7) in accordance with the internal resistance of the battery and the electromotive force of the battery which is measured in the non-loading condition just before the printing (step S6). As a result, it is possible to extend the voltage applying time period to the thermal head in response to the lowering of the output voltage of the battery so as not to make the printed result to be in a low density.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a printer, such as a portable printer, which is driven by power supply from a battery or an external power supply and prints characters, bar codes, and the like on paper by a thermal head.

[0002]

2. Description of the Related Art Conventionally, in a printer that performs printing using a thermal head, printing is performed by energizing a heating element provided in the thermal head. Therefore, the printing quality depends on the voltage and current capacity of the power supply. Therefore,
Normally, a power supply is specified, and a heating element is energized to perform printing within a range corresponding to the capability of the power supply.

As such a thermal printer, there is a portable printer which is driven by power supply from a battery and prints characters, bar codes, and the like by a thermal head. The portable printer is driven by power supply from a battery or an external power supply.

[0004]

Here, the battery is:
The output voltage gradually decreases as the charged amount decreases. For this reason, when the portable printer is driven by power supply from the battery, the printing conditions cannot always be kept constant.

[0005] In addition, batteries such as lithium ion and nickel hydride which are often used in portable printers are:
It has a deterioration characteristic in which the internal resistance increases by repeating charging and discharging.

Therefore, when a battery is used as a power source, in order to always obtain a constant printing quality, it is necessary to not only change the output voltage due to the printing rate, but also reduce the amount of stored power of the battery and increase the internal resistance. The decline must also be considered.

SUMMARY OF THE INVENTION It is an object of the present invention to obtain a constant print quality regardless of a change in output voltage.

[0008]

According to a first aspect of the present invention, there is provided a printer which receives power from a power supply and prints on a sheet by using a thermal head in which a large number of heating elements are arranged. Voltage measurement means for measuring a power supply voltage of the power supply in a state and a no-load state in which power is not supplied, and discrimination for determining a voltage application time to the thermal head according to a battery state detected from a measurement result of the voltage measurement means Means.

For example, by measuring the power supply voltage in a no-load state in which no heat is supplied to the heating element, the electromotive force of the battery, which is one of the indicators of the battery state, can be obtained. The internal resistance of the battery, which is another indicator of the battery state, can be calculated from the resistance and the power supply voltage in the load state where the several heating elements are energized. By changing the voltage application time, substantially constant print quality can be obtained irrespective of fluctuations in the output voltage of the battery.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A portable printer which is an embodiment of the printer of the present invention will be described with reference to FIGS.

First, FIG. 1 is a block diagram showing the electrical connection of each unit provided in the portable printer according to the present embodiment. The portable printer uses a battery 1 and an external power supply 2 as power supplies, and is driven by power supply from one of these power supplies.

The portable printer has an arithmetic unit 3, which includes a transport unit 4 and a printing unit 5 driven under the control of the arithmetic unit 3, an operation unit 6 for receiving an operation by an operator, and an external unit such as a personal computer. An interface 7 for communication, a label sensor 8 for detecting a label position, a thermistor 9, and a power supply voltage detection circuit 10 are connected.

The arithmetic unit 3 has a CPU 11 for executing various arithmetic processes and centrally controlling each unit.
A memory 12 composed of a plurality of ROMs and RAMs is connected to U11 via a bus line. The ROM is a medium for storing various programs.
Various processes are performed in accordance with the program stored in the OM. The RAM has a resist function, and temporarily stores various variable information.

The arithmetic unit 3 also includes an I / O 13 and an A / D
And a converter 14.

The transport unit 4 has a pulse motor 15 and transports a label as a sheet under the control of the arithmetic unit 3.

The printing section 5 has a thermal head 16,
Under the control of the arithmetic unit 3, the print data stored in the memory 12 is printed on the label.

The operation unit 6 has various switches such as a power switch 17 and a paper feed key 18.

FIG. 2 is a circuit diagram showing an equivalent circuit when the thermal head 16 is energized by the battery 1. The current flowing through this equivalent circuit is defined as I.

The equivalent circuit A of the thermal head 16 includes a resistor R by a heating element provided in the thermal head 16 and a resistor R ₀ corresponding to a wiring resistance in the thermal head 16 and a loss of the driver IC. The heating element is formed by arranging a large number of heating elements. The resistance R depends on the number of heating elements to be energized (hereinafter referred to as the number of elements),
The resistance value increases as the number of elements decreases, and decreases as the number of elements increases.

The equivalent circuit B of the battery 1 includes an electromotive force E of the battery 1 and an internal resistance r. The voltage between terminals of the battery 1 is assumed to be V. The electromotive force E decreases as the charged amount of the battery 1 decreases. The internal resistance r increases as the battery 1 deteriorates due to repeated charging and discharging, and lowers the output voltage, that is, the inter-terminal voltage V when energized. The electromotive force E and the inter-terminal voltage V are measured by the power supply voltage detection circuit 10.

In this equivalent circuit, the thermal head 16 side
The resistance value of the entire B is represented by a resistance R and a resistance R ₀And are connected in series
R + R₀And these resistance R and resistance
Anti-R₀The voltage applied to the whole is the terminal voltage V. did
Therefore, I = V / (R + R₀) ……………………………. On the battery 1 side, I = (EV) / r...... In other words, from the equation and the equation 2, this equivalent circuit
Is I = V / (R + R₀) = (E−V) / r... By transforming this equation, r = (R + R₀) · (E−V) / V.........

When the printing rate is 0%, that is, in a no-load state where no heating element is energized, no current flows through the equivalent circuit of FIG. 2 and the current I = 0. By substituting this into the equation, 0 = (E−V) / r, so that E = V. That is, in a no-load state, the terminal voltage V is equal to the electromotive force E.

By substituting I = 0 into the equation, the resistance R in the no-load state is considered to be virtually R = ∞.

The measurement of the internal resistance r of the battery 1 is performed in the state of the load applied current I ≠ 0. However, since the resistance R ₀ and the internal resistance r depend on the current I, the current I is changed by changing the number of elements to be energized several times, and the internal resistance r corresponding to each current I is calculated. And the internal resistance r must be obtained. The resistors R having different numbers of elements used in the measurements several times are stored in the nonvolatile memory.

Further, since the internal resistance r varies depending on the ambient temperature, a data table for the temperature is obtained in advance by a test and is prepared, and if the data table is reflected in the calculation, the internal resistance r can be calculated more accurately.

FIG. 3 is a flowchart showing a flow of issuing a label by changing the energizing time of the heating element according to the power supply voltage. This series of processing is executed by the CPU 11 based on a program stored in the ROM.

When the power is turned on by the power switch 17, first, the voltage V between terminals is measured when the thermal head 16 is not loaded and energized (step S1). At no load, the electromotive force E is measured by measuring the voltage V between terminals.
Is obtained. At the time of energization, the number of elements is changed a predetermined number of times, and the terminal voltage V, that is, the output voltage is measured in each case. Then, the internal resistance r is calculated based on each measurement value obtained in Step 1 (Step S2).

Next, the label is fed by paper feed (step S3), and the print data reception wait state is set.

When print data is received (step S
4), drawing data is created (step S5). Then, the terminal voltage V at the time of no load is measured (Step S).
6) The electromotive force E at this time is obtained. Based on the electromotive force E, the internal resistance r calculated in step S2, the resistance R calculated from the number of elements in each line, the ambient temperature, and the like,
The optimum energizing time of the heating element for obtaining a constant printing quality is calculated for each line (step S7). And 1
For each line, transfer of drawing data to the thermal head 16, energization and paper feeding according to the calculated energization time are repeated, and a label is issued (step S8). After one label is issued, the print data reception wait state is set, and the processes in steps S4 to S8 are continued until the power is turned off.

In such a configuration, by calculating the internal resistance r when the power is turned on, it is possible to cope with a decrease in the output voltage due to an increase in the internal resistance r due to the deterioration of the battery 1. Further, by measuring the electromotive force E immediately before printing in step S6, it is possible to take measures such as lengthening the energizing time in accordance with the decrease in the electromotive force E associated with the decrease in the charged amount of the battery 1.

According to this embodiment, the energy applied to the heating element can be accurately controlled, and a constant printing quality can be always maintained.

When the printing rate is high, since a large number of heating elements are energized, the load resistance value of the heating elements becomes extremely low, so that the voltage drop due to the internal resistance of the battery 1 increases, and the energy Loss cannot be ignored. Since the battery 1 used in the portable printer has a small current capacity, the phenomenon that the output voltage fluctuates due to the printing rate appears more remarkably. However, according to the present embodiment, since the heating elements are energized for the energization time corresponding to the number of elements calculated in step S7, even if the output voltage fluctuates due to the printing rate, the printing quality is not reduced. The effect can be eliminated.

Further, in the present embodiment, step S1
Then, a predetermined number of heating elements are energized for measuring the internal resistance r. At this time, the label in contact with the thermal head 16 is partially colored by the energized heating elements. Since the dropped label is discharged and discarded at the time of label cueing in step S3,
no problem. Since the cueing of the label is an operation that cannot be omitted and has been conventionally performed at the start of printing, the label is not wasted as compared with the conventional printing method.

In this embodiment, the case where the battery 1 is used has been described. However, the present invention can also be carried out when an external power source 2 having a small capacity is used.

In an actual product, electronic components such as the arithmetic unit 3 other than the thermal head 16 are connected to the battery 1, but since the power consumed by the thermal head 16 and the like is sufficiently small, these components are not used. The power consumption of the electronic components is negligible.

[0036]

According to the first aspect of the present invention, the power supply voltage is measured in the load state in which the heating element is energized and in the non-load state in which the heating element is not energized, and the voltage application time to the thermal head is determined according to the measurement result. In addition, the voltage application time to the thermal head can be changed according to the output voltage, so that almost the same print quality can always be obtained. In particular, when a battery is used, it is effective against a decrease in power supply voltage due to an increase in internal resistance due to deterioration due to repeated storage and discharge and a decrease in the amount of stored power due to use of the printer.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an electrical connection of each unit included in a portable printer according to an embodiment of the present invention.

FIG. 2 is a circuit diagram showing an equivalent circuit when a thermal head is energized.

FIG. 3 is a flowchart illustrating a flow of issuing a label by changing the energization time of a heating element according to a power supply voltage.

[Explanation of symbols]

 1 power supply, battery 16 thermal head

Claims (1)

[Claims] 1. A printer which receives power supply from a power supply and prints on paper by a thermal head in which a large number of heating elements are arranged, wherein a power supply voltage of the power supply in a load state in which the heating elements are energized and in a no-load state in which the heating elements are not energized. Voltage measuring means for measuring
A differentiator configured to determine a voltage application time to the thermal head according to a battery state detected from a measurement result of the voltage measuring unit.