JPH0768825A - Thermal head energization control device - Google Patents

Abstract

(57) [Abstract] [Purpose] By modulating the duty ratio of the head strobe signal that controls the energization of the thermal head based on the number of dots on the thermal head, the print density due to voltage drop due to wiring resistance etc. at the time of head on Effectively prevent the decrease of. [Structure] The CPU 1 obtains the number of head-on dots of the entire thermal head 9 based on the print data and stores it in the RAM 2. The strobe signal control device 6 changes the duty ratio of the head strobe signal based on the number of head-on dots and supplies it to the head driver 8. The head driver 8 drives the thermal head 9 based on the print data and the dot strobe signal from the strobe signal controller 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal head energization control device for controlling an energization time to a thermal head in a word processor equipped with a thermal printer.

[0002]

2. Description of the Related Art In recent years, a thermal printer has been the mainstream as a printing device for a word processor. In this thermal printer, a voltage is applied to a thermal head by using a volume in order to change the printing density. However, this kind of thing has drawbacks in terms of cost, etc.
Conventionally, there is one in which the print density is controlled by software by changing the energization time of the head according to the print density that is arbitrarily set in advance. As one of them, the present applicant has previously proposed a thermal head energization control device (Japanese Patent Application No. 4-1) that controls the energization time of the head according to the print density.
46831) was proposed. FIG. 3 shows this thermal head energization control device in principle. The thermal head energization control device controls the energization time of the thermal head according to the energization history and the print density arbitrarily designated by the user. The following history calculation is performed in parallel while the thermal head is energized. As described above, the history correction is actually performed in order to prevent the print unevenness due to the heat accumulation of the head, but in the energization control device shown in FIG. 3, the history correction is not shown in order to simplify the description. Therefore, only the point of controlling the energization time according to the print density will be described below.

The CPU 1 controls the overall operation of the thermal head energization control device according to various programs. When a print command is given from a keyboard or the like, the CP 1
U1 is print data PD0 stored in RAM2,
Of the PD1 ... PDn, the leading print data PD0 is read out and fetched through the memory controller 3, and the print density data in the RAM 2 arbitrarily designated by the user is fetched through the memory controller 3. Here, the CPU 1 gives the print data fetched from the RAM 2 to the print control device 4, and also searches the table memory 5-1 in the ROM 5 based on the print density data. The table memory 5-1 stores head strobe time data for controlling energization time for each print density, and the CPU 1 reads the head strobe time data corresponding to the print density read from the RAM 2 via the memory controller 3 to the table memory 5. -1 reading, strobe signal control device 6
Give to.

The basic clock oscillating device 7 oscillates and outputs a basic clock signal defining the operation timing of the entire thermal head energization control device, and supplies it to the CPU 1, print control device 4, and strobe signal control device 6. The print control device 4 parallelizes the print data sent from the CPU 1
Serial conversion and sending to head driver 8 and CP
The head strobe signal is given to the strobe signal control device 6 by the command sent from U1. This head strobe signal controls the energization of the entire thermal head by controlling the on / off of the entire thermal head. The strobe signal control device 6 is sent from the table memory 5-1 of the ROM 5 under the control of the CPU 1. The strobe signal is modulated by changing the duty ratio of the strobe signal based on the incoming head strobe time data, and is supplied to the head driver 8. The head driver 8 drives the thermal head 9 by the print data sent from the print controller 4 and the head strobe signal sent from the strobe signal controller 6.

In the thermal head energization control device having such a configuration, the print data (1 byte) read from the RAM 2 corresponds to one column of the thermal head 9 (for example, print data PD0 to PD11 = 96 dots = 12 bytes). Minute), the CPU 1 turns on the head strobe signal output from the print control device 4. The head strobe signal is modulated by the strobe signal control device 6 based on the print density-specific head strobe time data in the table memory 5-1 and sent to the head driver 8. Therefore, the head driver 8 prints the print data and the head strobe signal. The thermal head 9 is driven based on

After the thermal head 9 is turned on in this way, the CPU 1 causes the ROM via the memory controller 3.
5, the head energization time data is read, and after waiting until the time corresponding to this data elapses, the print control device 4
The head strobe signal output from is turned off. One line is printed by repeating such an operation until all the print data in the RAM 2 is printed.

[0007]

In the thermal head energization control device having the above-described structure, when the head is energized, the head power source 11 has a connecting portion 12 such as a cable and a connector, and a head driver as shown in FIG. 8 is supplied to the thermal head 9 via a voltage source 8, and a voltage drop occurs due to resistance components such as wiring resistance and contact resistance from the head power supply 11 to the connecting portion 12, the head driver 8 and the thermal head 9, respectively. The energy supplied to will be reduced. That is, assuming that the voltage of the head power supply 11 is VH, the resistance value of the thermal head 9 is R, the positive side voltage of the head power supply is V1, and the ground side voltage is V2, the energy E supplied to the thermal head 9 is E = (VH-V1-V2) ² / R. In particular, this voltage drop becomes large when the black print ratio is high, that is, when all the dots of the thermal head 9 are on, and there is a problem that the print becomes thin. An object of the present invention is to modulate the duty ratio of a head strobe signal for controlling energization of a thermal head based on the number of dots on the thermal head,
It is possible to effectively prevent a decrease in print density due to a voltage drop due to wiring resistance or the like when the head is turned on.

[0008]

The means of the present invention are as follows. (1) The head strobe signal generating means generates a head strobe signal for controlling energization of the entire thermal head. (2) The calculating means calculates the number of head-on dots of the entire thermal head based on the print data. (3) The strobe signal modulating means changes the duty ratio of the head strobe signal generated by the head strobe signal generating means based on the number of head-on dots calculated by the calculating means. The strobe signal modulating means may change the duty ratio of the head strobe signal based on the print density designated in advance together with the number of head-on dots calculated by the calculating means. (4) The head driving means drives the thermal head from the head strobe signal and print data modulated by the strobe signal modulating means.

[0009]

The operation of the means of the present invention is as follows. Now, at the start of printing, the number of on-dots of the entire thermal head is calculated based on the print data. Then, the duty ratio of the head strobe signal is changed based on the number of head-on dots, and the thermal head is driven based on the head strobe signal and the print data modulated by the duty ratio. By changing the duty ratio of the head strobe signal in this manner, the ratio of turning on / off the thermal head changes according to the on / off state of the signal. Therefore, the print density control is performed based on the number of on-dots of the thermal head. Therefore, by modulating the duty ratio of the head strobe signal that controls the energization of the thermal head based on the dot-on number of the thermal head, it is possible to effectively prevent the print density from decreasing due to voltage drop due to wiring resistance when the head is on. can do.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment will be described below with reference to FIGS. FIG. 1 is a block diagram showing the configuration of a thermal head energization control device. Since the thermal head energization control device of FIG. 1 has basically the same configuration as the thermal head energization control device shown in FIG. 3, basically the same parts are denoted by the same reference numerals, and the description thereof will be omitted. It shall be. In the thermal head energization controller of this embodiment, the RAM 2 has print data PD0, PD1, ... PD.
In addition to n and printing density data preset by the user, the number of ON dots of the thermal head is stored.
Here, the CPU 1 prints each print data PD of 1 byte.
The number of ON dots of 0, PD1, ... Is obtained for each byte, and this is added for each vertical column of the thermal head 9 (all dots = 96 dots = 12 bytes), and the addition result is stored in the RAM2. The data is the number of dots for the head ON. That is, the head ON dot number data in the RAM 2 is the data that becomes the ON dot number of the entire thermal head 9 when the print data (12 bytes) for one vertical column of the thermal head 9 is read from the RAM 2. is there.

A table memory 5-1 in the ROM 5 is also provided.
The head strobe time data for energization time control is stored for each print density. In the present embodiment, the head strobe time data for each print density is further stored for each ON dot number of the entire thermal head 9. It is composed. For example, the number of ON dots of the entire thermal head 9 corresponding to the print density of 100% is “0”, “1”,
Head strobe time data is stored for each "2", ... "96", and then the number of ON dots of the entire thermal head 9 corresponding to the print density of 75% is "0", "1", "2" ,.
... The head strobe time data is stored for each "96",
Similarly, head strobe time data is stored for each print density and the number of ON dots.

Next, the operation of this embodiment will be described. First,
Upon receiving the print command from the keyboard or the like, the CPU 1 clears the head ON dot number in the RAM 2 via the memory control device 3. Next, the CPU 1 sends the print data PD0 for the first 1 byte from the RAM 2 via the memory controller 3.
Is read and sent to the print control device 4. As a result, the print control device 4 performs parallel / serial conversion of the print data PD0 and sends it to the head driver 8. At the same time, CPU1
Determines the number of on-dots of this print data PD0, RAM
It is added to the head ON dot number data in 2 (initially 0), and the result is written in the RAM 2.

The CPU 1 repeats such operation while sequentially reading the print data from the RAM 2 byte by byte. As a result, one column of the thermal head 9 in the vertical direction from the RAM 2, that is, print data PD0 to PD11 = 96 dots =
When 12 bytes of print data is read, the CPU
1 reads out the print density data and the head ON dot number data from the RAM 2, and based on this, obtains the read address for the table memory 5-1 in the ROM 5,
The memory controller 3 is given this read address. Then, the memory control device 3 accesses the table memory 5-1 according to the read address, reads the corresponding head strobe time data, and gives it to the CPU 1. For example, if the print density is 75%, the thermal head 9
If the total number of head-on dots is "96", the corresponding head strobe time data is T75. 9
6 is read from the table memory 5-1 and given to the CPU 1.

Then, the CPU 1 sends this head strobe time data to the strobe signal controller 6 and
The head strobe signal output from the print control device 4 is turned on. As a result, the strobe signal controller 6 sends the head strobe signal from the print controller 4 to the CPU 1
Modulation based on the head strobe time data from
The duty ratio is changed. Here, the head driver 8 drives the thermal head 9 based on the print data sent from the print control device 4 and the head strobe signal sent from the strobe signal control device 6.

Next, the CPU 1 turns on the thermal head 9 as described above, then reads the head strobe time data from the ROM 5 via the memory control device 3,
After waiting for the time indicated by the data to pass, the print controller 4 is controlled to turn off the head strobe signal, and the dot printing for one vertical column of the thermal head 9 is completed. After that, the CPU 1 clears the number of head-on dots in the RAM 2 again, and then repeats the above operation to perform one-line printing.

FIG. 2 shows an example of the output waveform of the head strobe signal output from the strobe signal control device 6. Here, when the print density is 50%, the print density is 50% when the number of ON dots of the head is 48 dots. It is an example of an output waveform in which the head strobe signal is modulated so that At this time, when the number of ON dots of the head is 0, the duty ratio of the head strobe signal is set to be lower than that because the influence of the voltage drop due to the wiring resistance and the contact resistance is small. When the number of ON dots is 96, the influence of the voltage drop is large, so the duty ratio is set to be high. Here, when the influence of the voltage drop due to the wiring resistance or the like is about +/− 5% in the minimum to maximum range, the duty ratio of the head strobe signal waveform is set to − / + 5% to cause the voltage drop. I try to prevent uneven printing.

In the above embodiment, the print density is 100%.
%, 75%, etc. are set stepwise, but the number is arbitrary. Further, the above embodiment is applicable to a thermal head energization control device that controls the energization time of the thermal head according to the energization history and the set print density and also performs history calculation in parallel during energization of the thermal head. Is.

[0018]

According to the present invention, the duty ratio of the head strobe signal for controlling the energization of the thermal head is modulated based on the dot-on number of the thermal head, so that the voltage drop due to the wiring resistance or the like at the time of head-on is caused. It is possible to effectively prevent a decrease in print density, and it is possible to obtain good print results without print unevenness.

[Brief description of drawings]

FIG. 1 is a block configuration diagram of a thermal head energization control device according to an embodiment.

FIG. 2 is a diagram showing a head strobe signal waveform based on the number of head ON dots.

FIG. 3 is a block diagram showing the principle of a thermal head energization control device, which is the premise of this embodiment.

FIG. 4 is a diagram for explaining a problem of the thermal head energization control device shown in FIG.

[Explanation of symbols]

 1 CPU 2 RAM 3 Memory Controller 4 Print Controller 5 ROM 5-1 Table Memory 6 Strobe Signal Controller 7 Basic Clock Oscillator 8 Head Driver 9 Thermal Head

Claims (2)

[Claims] 1. A head strobe signal generating means for generating a head strobe signal for controlling energization of the entire thermal head, a calculating means for calculating the number of head-on dots of the entire thermal head based on print data, and the calculating means. Strobe signal modulating means for changing the duty ratio of the head strobe signal generated by the head strobe signal generating means based on the calculated number of head-on dots, and the head strobe signal and print data modulated by the strobe signal modulating means. And a head driving means for driving the thermal head, and a thermal head energization control device. 2. The strobe signal modulating means is adapted to change the duty ratio of the head strobe signal based on a print density designated in advance together with the number of head-on dots calculated by the calculating means. The thermal head energization control device according to claim 1.