JP2000326539A - Printing apparatus and printing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control a printing density by setting a pulse width of control pulses to meet a decrease in impressed voltage of a thermal head. SOLUTION: A value obtained by multiplying by a coefficient 0.8 a difference of an impressed voltage value of a thermal head before printing and a minimum voltage value of the impressed voltage value of the thermal head during printing is subtracted from the impressed voltage value of the thermal head before printing, thereby obtaining a threshold value. When the impressed voltage value of the thermal head during printing (detect voltage) is larger than the threshold value, a pulse width of control pulses is obtained on the basis of the threshold value. When the impressed voltage value of the thermal head during printing is the threshold value or smaller, the pulse width of control pulses is obtained on the basis of the impressed voltage value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a printing apparatus and a printing method, and more particularly, to a printing method in which when printing is performed using a thermal head, a voltage applied to the thermal head is controlled to suppress variations in print density. The present invention relates to an apparatus and a printing method.

[0002]

2. Description of the Related Art Conventionally, in a label printer that performs printing using a thermal head, in order to equalize the thermal energy of the thermal head and suppress variations in print density, the value of a voltage applied to the head is reduced to a predetermined value. CPU (central pro) that operates according to the control program
sensing unit), a pulse width of a control pulse applied to the thermal head is determined based on the read voltage value, and feedback control for applying a control pulse having the determined pulse width to the thermal head is performed.

[0003]

However, since there is a time lag between the control pulse supplied to the thermal head and the value of the applied voltage read from the thermal head by the CPU, the control pulse supplied to the thermal head is controlled. And the print density deviates from a predetermined density.

That is, since the timing at which the CPU reads the voltage value applied to the thermal head is during the printing operation of the thermal head, a large load is imposed on the power supply of the label printer and the power supply capacity is small during the printing operation. In this case, a voltage drop phenomenon may occur. In such a device, the voltage value read by the CPU when the applied voltage of the thermal head is changing after the start of printing while decreasing is lower than the voltage value read by the CPU when the applied voltage is reduced to the minimum value. Will also be higher.

Accordingly, when the CPU performs feedback control of the control pulse supplied to the thermal head based on the voltage value read from the thermal head while the voltage is changing while decreasing, the print density deviates from the predetermined density. In some cases.

The present invention has been made in view of such a situation, and it is possible to effectively control the pulse width of the control pulse supplied to the thermal head even if the applied voltage decreases after the start of printing. It is to be.

[0007]

According to a first aspect of the present invention, there is provided a printing apparatus for performing printing using a thermal head, wherein a pulse supply means for supplying a control pulse to the thermal head and the thermal head performs printing. A first detecting means for detecting a voltage value applied to the thermal head; and a second detecting means for detecting a voltage value applied to the thermal head while the thermal head is performing printing. Means, storage means for storing the voltage value detected by the first detection means, and the voltage value detected by the second detection means, and detection by the first detection means stored in the storage means. Calculating means for calculating a predetermined reference voltage value based on the detected voltage value and the minimum value of the voltage value detected by the second detecting means; and a voltage value detected by the second detecting means. Comparing means for comparing the magnitude with the magnitude of the reference voltage value, and control means for controlling a pulse width of a control pulse supplied from the supply means to the thermal head based on a comparison result by the comparison means. I do. The calculating means multiplies a calculation result obtained by subtracting the lowest value of the voltage value detected by the second detecting means from the voltage value detected by the first detecting means by a predetermined coefficient. The calculation result obtained by subtracting the calculation result obtained from the voltage value detected by the first detection means can be used as the reference voltage value. The printing method according to claim 3, wherein in the printing method for performing printing using the thermal head, a pulse supply step of supplying a control pulse to the thermal head, and the pulse applied to the thermal head before the thermal head performs printing. A first detection step of detecting a voltage value applied to the thermal head, a second detection step of detecting a voltage value applied to the thermal head while the thermal head is performing printing, and a first detection step. A storage step of storing the detected voltage value, the voltage value detected in the second detection step, a voltage value detected in the first detection step, stored in the storage step, and a second detection step A calculating step of calculating a predetermined reference voltage value based on the lowest value of the voltage value detected in A comparison step of comparing the magnitude of the detected voltage value with the magnitude of the reference voltage value; and a control step of controlling a pulse width of a control pulse supplied to the thermal head in the supply step based on a comparison result in the comparison step. And characterized in that: In the printing apparatus and the printing method according to the present invention, a control pulse is supplied to the thermal head to detect a voltage value applied to the thermal head before the thermal head performs printing, and the thermal head performs printing. During printing, the voltage value applied to the thermal head is detected, the detected voltage value is stored, and the voltage value applied to the thermal head before the thermal head performs printing and the thermal head A predetermined reference voltage value is calculated based on the lowest voltage value applied to the thermal head during the printing operation, and the predetermined reference voltage value is applied to the thermal head while the printing operation is performed. The magnitude of the applied voltage value is compared with the magnitude of the reference voltage value, and the pulse width of the control pulse supplied to the thermal head is controlled based on the comparison result.

[0008]

FIG. 1 is a block diagram showing a configuration example of an embodiment of a label printer to which a printing apparatus according to the present invention is applied. As shown in the figure, in the present embodiment, a ROM (read
main memory 1 composed of only memory
And a RAM for storing various data (random a
a storage device 2 (storage unit) including a memory (access memory), a thermal head 5 for performing printing, and a voltage detection unit 4 (first detection unit and second detection unit) for detecting a voltage applied to the thermal head 5. A / A that converts the value of the applied voltage detected by the voltage detection unit 4 into a digital signal
The head operates in accordance with the D converter 3 and a control program stored in the main storage device 1, and based on the applied voltage value supplied from the A / D converter 3, a head control pulse having a predetermined pulse width (hereinafter referred to as appropriate) , A control pulse), which is supplied to the thermal head 5 or controls each part.
PU (central processing uniti)
t) 6 (arithmetic means, comparison means, control means).

The control pulse supplied to the thermal head 5 is for applying heat energy to a heating element constituting the thermal head 5 to warm it. Thermal head 5
Is constituted by heating elements corresponding to pixels (dots) for one line. Each heating element generates heat in accordance with a character or a figure to be printed, so that a predetermined character or character is formed on heat-sensitive paper which changes to black by heat. The figures are formed line by line.

Next, the operation of the embodiment shown in FIG. 1 will be described with reference to the flowchart of FIG. 2 and the timing chart of FIG. FIG. 2 is a flowchart showing the operation of the embodiment shown in FIG. 1, and FIG.
5 is a timing chart showing the operation of the embodiment shown in FIG.

As shown in FIG. 3, the voltage value of the applied voltage applied to the thermal head 5 decreases after the start of printing, changes to a substantially constant value when the lowest voltage value is reached, and changes when the printing is completed. Returns to the previous voltage value. The black circles indicate the applied voltage (head voltage) of the thermal head 5 in each line.

In FIG. 2, first, at step S1
In accordance with the control program stored in the main storage device 1, the CPU 6 instructs the voltage detection unit 4 to apply the voltage value of the applied voltage applied to the thermal head 5 before printing (voltage before printing (FIG. 3) ) Is detected.

The voltage detector 4 receiving this command from the CPU 6 detects the voltage value of the applied voltage applied to the thermal head 5 and supplies the detected voltage value to the A / D converter 3. The A / D converter 3 converts the voltage value of the applied voltage of the thermal head 5 supplied from the voltage detection unit 4 into digital data and supplies the digital data to the CPU 6.

The CPU 6 stores data corresponding to the value of the applied voltage supplied from the A / D converter 3 in the storage device 2.
And store it.

Next, in step S2, under the control of the CPU 6, the thermal head 5 starts printing on a label (FIG. 3) made of a predetermined thermal paper. Next, in step S3, the CPU 6 instructs the voltage detector 4 to detect the applied voltage during printing of the thermal head 5. Voltage detection unit 4 receiving this command from CPU 6
Detects the voltage value of the applied voltage applied to the thermal head 5 and supplies the detected voltage value to the A / D converter 3. The A / D converter 3 converts the voltage value of the applied voltage of the thermal head 5 supplied from the voltage detection unit 4 into digital data and supplies the digital data to the CPU 6. The CPU 6 supplies data corresponding to the voltage value of the applied voltage supplied from the A / D converter 3 to the storage device 2 and stores the data.

Then, in step S4, the CPU 6
Is the voltage value of the voltage value of the applied voltage during printing of the thermal head 5 stored in the storage device 2 in step S3 and the voltage value of the applied voltage during printing that was detected immediately before, whichever is lower. Is the lowest voltage level,
It is stored in the storage device 2.

Next, proceeding to step S5, the CPU 6
The voltage value of the lowest voltage level obtained in step S4 is subtracted from the voltage value of the applied voltage before printing read from the storage device 2, and the obtained result is set as a voltage difference ΔV. That is, the voltage difference ΔV is calculated by the following equation (1). The calculated voltage difference ΔV is supplied to the storage device 2 and stored.

ΔV = voltage value of applied voltage before printing−voltage minimum level (1)

Next, a result obtained by subtracting a value obtained by multiplying the voltage difference ΔV by, for example, a coefficient of 0.8 from the voltage value of the applied voltage before printing is set as a threshold value. That is, the threshold is calculated by the following equation (2). The calculated threshold value is supplied to the storage device 2 and stored.

Threshold value = voltage value of applied voltage before printing−0.8 × ΔV (2)

The voltage difference ΔV obtained by equation (1) and the threshold value obtained by equation (2) are updated once for each line, except for the first line of the first label after printing starts. As a result, each of them takes a substantially constant value, and does not vary much between lines.

Next, in step S6, the voltage value of the applied voltage during the printing of the thermal head 5 detected by the voltage detection unit 4 in step S3 (detected voltage ( (Fig. 3))
Is compared with the threshold value calculated in step S5, and it is determined which is larger.

When the CPU 6 determines that the value of the detected voltage is larger than the threshold value, the process proceeds to step S7, where the CPU 6 uses the threshold value to control the pulse of the control pulse supplied to the thermal head 5. Set the width. Then, a control pulse having the set pulse width is generated and supplied to the thermal head 5. Then, after printing of this line is performed by the thermal head 5, the process proceeds to step S9.

On the other hand, when the CPU 6 determines that the value of the detected voltage is smaller than or equal to the threshold value,
Proceeding to step S8, the CPU 6 sets the pulse width of the control pulse supplied to the thermal head 5 using the detected voltage. Then, a control pulse having the set pulse width is generated and supplied to the thermal head 5. Then, after printing of this line is performed by the thermal head 5, the process proceeds to step S9.

In general, the time for supplying current to the thermal head 5 is changed according to the printing rate of the character to be printed, and the time for warming the thermal head 5 is controlled. For example, when the printing rate is large (for example, when there are ruled lines under characters and there are many black portions), the time for supplying current to the thermal head 5 is increased, and the time for warming the thermal head 5 is increased. However, even when the printing rate is high, the heat energy required for printing is obtained.

The pulse width of a control pulse that can be supplied to the thermal head 5 before printing one line, that is, the maximum value of the time for supplying a current to the thermal head 5 is fixed and exceeds the maximum value. Within such a range, the pulse width of the control pulse is controlled in accordance with the printing rate.

In step S9, the CPU 6 determines whether the line printed by the thermal head 5 is the last line to be printed. If it is determined that the line printed by the thermal head 5 is not the last line to be printed, the process proceeds to step S10, in which the CPU 6 rotates a platen roller or the like (not shown) to convey the label by one line. . Thereafter, the process returns to step S3, and the processes after step S3 are repeatedly executed.

On the other hand, if it is determined that the line printed by the thermal head 5 is the last line to be printed, the processing is terminated. Thereafter, when printing the next label, printing is performed on the label.

In the timing chart shown in FIG. 3, the black circles indicate the values of the head voltage in each line to be printed (the thermal head 5 detected by the voltage detector 4).
And the head voltage drops after printing on the label is started. In this example, the head voltage values of the lines 1 to 3 are respectively larger than the threshold value. Therefore, while printing the lines 1 to 3, the CPU 6 supplies a control pulse having a pulse width set based on the threshold value to the thermal head 5.

Then, in this example, after line 4,
Since the value of the head voltage is smaller than the threshold value, the CPU 6 applies the detection voltage (head voltage)
Is supplied to the thermal head 5 with a pulse width set based on the above. The thermal head 5 is heated by the control pulse supplied from the CPU 6, performs a printing operation, and when the printing of the last line is completed, the value of the head voltage returns to the original value.

As described above, the head voltage at the time of the printing operation is read at regular intervals, the change of the voltage level is monitored, and the minimum voltage level when the voltage is completely reduced is obtained. Then, a threshold value of a voltage level used for feedback control is set based on the minimum voltage level and a voltage level before the voltage read before printing decreases, and when the head voltage value is lower than the threshold value. The pulse width of the control pulse is set based on the value of the head voltage, and when the head voltage is higher than the threshold value, the pulse width of the control pulse is set based on the minimum voltage value of the head voltage read in the past.

Therefore, the pulse width of the control pulse can be set based on the minimum voltage value until the head voltage drops to a value lower than the threshold value after the start of printing. The control pulse having an appropriate pulse width can be supplied to the thermal head 5 while the applied voltage 5 is higher than the threshold value. Thereby, the print density can be made substantially constant at a predetermined density.

Further, since the print density can be controlled in accordance with a decrease in the voltage applied to the thermal head 5 irrespective of the type of power supply (A / C adapter, battery, etc.), the application of the thermal head 5 It is possible to suppress the change in the print density due to the fluctuation of the voltage and make the print density almost constant.

In the above embodiment, the case where the printing apparatus of the present invention is applied to a label printer has been described. However, the present invention can be applied to other printing apparatuses.

The specific numerical values used in the above embodiment are examples, and the present invention is not limited to these values.

[0036]

As described above, according to the printing apparatus and the printing method of the present invention, a control pulse is supplied to the thermal head, and before the thermal head performs printing, the voltage value applied to the thermal head is reduced. Detects and detects the voltage value applied to the thermal head while the thermal head is performing printing, stores the detected voltage value, and applies the voltage value to the thermal head before the thermal head performs printing. A predetermined reference voltage value is calculated based on the voltage value and the lowest voltage value applied to the thermal head while the thermal head is performing printing, and the thermal head performs printing. During the operation, the magnitude of the voltage value applied to the thermal head is compared with the magnitude of the reference voltage value, and based on the comparison result, the pulse of the control pulse supplied to the thermal head is compared. Since so as to control the width, it is possible to suppress variations in print density due to variations in the applied voltage being applied to the thermal head.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration example of an embodiment of a label printer to which a printing apparatus according to the invention is applied.

FIG. 2 is a flowchart for explaining the operation of the embodiment of FIG. 1;

FIG. 3 is a timing chart for explaining the operation of the embodiment of FIG. 1;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Main storage device 2 Storage device 3 A / D converter 4 Voltage detector 5 Thermal head 6 CPU

Claims (3)

[Claims] 1. A printing apparatus for performing printing using a thermal head, comprising: a pulse supply unit configured to supply a control pulse to the thermal head; and a voltage applied to the thermal head before the thermal head performs printing. First detection means for detecting a voltage value; second detection means for detecting a voltage value applied to the thermal head while the thermal head is performing printing; and the first detection. Said voltage value detected by the means;
Storage means for storing the voltage value detected by the second detection means; the voltage value detected by the first detection means stored in the storage means; and the second detection means Calculating means for calculating a predetermined reference voltage value based on the lowest value of the voltage value detected by the second detecting means; the magnitude of the voltage value detected by the second detecting means; and the magnitude of the reference voltage value. And a control unit for controlling a pulse width of the control pulse supplied to the thermal head by the supply unit based on a comparison result by the comparison unit. 2. The arithmetic unit according to claim 1, wherein the arithmetic unit obtains an arithmetic result obtained by subtracting a minimum value of the voltage value detected by the second detecting unit from the voltage value detected by the first detecting unit. An operation result obtained by subtracting an operation result obtained by multiplying a predetermined coefficient from the voltage value detected by the first detecting means is used as the reference voltage value. The printing device according to claim 1. 3. A printing method for performing printing using a thermal head, comprising: a pulse supplying step of supplying a control pulse to the thermal head; and a voltage applied to the thermal head before the thermal head performs printing. A first detection step of detecting a voltage value; a second detection step of detecting a voltage value applied to the thermal head while the thermal head is performing printing; and the first detection step. And a storage step of storing the voltage value detected in the second detection step, and the voltage value detected in the first detection step, stored in the storage step And calculating a predetermined reference voltage value based on the minimum value of the voltage value detected in the second detection step. A comparing step of comparing the magnitude of the voltage value detected in the second detecting step with the magnitude of the reference voltage value, based on a comparison result in the comparing step, A control step of controlling a pulse width of the control pulse supplied to the thermal head.