JPH0852894A - Thermal head driving method and apparatus - Google Patents

Abstract

(57) [Abstract] [Purpose] It is an object to provide a driving method and a driving apparatus for a thermal line head that eliminates density unevenness due to sticking. In a printer for forming an image on a recording sheet by using a thermal line head having a plurality of heating resistors arranged linearly, the heating resistors are divided into a plurality of blocks, and each block is divided into a plurality of blocks. Driving means capable of independently driving heat generation, printing rate determining means for determining a printing rate based on print data input to the thermal head, and heating the plurality of blocks according to the printing rate. And a drive timing determining means for determining a drive timing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to drive control of a thermal printer head for forming an image with a thermal line head.

[0002]

2. Description of the Related Art Conventionally, there has been known a printer for forming an image on a thermal paper of a predetermined size by using a thermal line head in which heating resistors are linearly arranged. Usually, the thermal line head is divided into a plurality of blocks and drive-controlled. That is, an image for one line is formed by sequentially driving a plurality of blocks at different times,
A two-dimensional image is formed on the thermal paper by conveying the thermal recording paper at a predetermined speed in synchronization with this.

[0003]

In such a printer, only a specific block is driven with a high printing rate (ratio between the total number of heating resistors in the block and the number of heating resistors driven to generate heat for printing). If so, a phenomenon called so-called sticking occurs. Sticking is a phenomenon in which the thermal paper is stuck to the thermal head due to a high printing rate, which causes unevenness in the feeding of the thermal paper. That is, this is a phenomenon in which the image formed by the heating resistors of the block having a high printing rate becomes darker as a result compared with the image of the other blocks. When such a sticking phenomenon occurs, an image having uneven density is formed as a whole, and therefore, improvement has been desired in the printer of the above type.

SUMMARY OF THE INVENTION In view of the above circumstances, it is an object of the present invention to provide a driving method and a driving device for a thermal line head that eliminates uneven density due to sticking.

[0004]

In order to achieve the above object, the thermal head driving device of the present invention uses a thermal line head having a plurality of linear heating resistors to form an image on recording paper. In the forming printer,
A printing rate that divides the plurality of heating resistors into a plurality of blocks and can independently drive heat generation in each block and a printing rate that determines a printing rate based on print data input to a thermal head. It is characterized by having a determining means and a timing determining means for determining the timing of driving the plurality of blocks to generate heat in accordance with the printing rate.

Further, according to the thermal head driving method of the present invention, a thermal line head having a plurality of heating resistors arranged linearly is used to input the thermal head in a printer for forming an image on recording paper. The printing rate is determined based on the printing data, and the plurality of heating resistors are
It is characterized in that it is divided into a plurality of blocks according to the printing rate, and the plurality of divided blocks are driven at different timings.

[0006]

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

FIG. 1 is a perspective view showing the appearance of a thermal line printer 1 as an embodiment of the present invention. The printer 1 of the present embodiment uses a thermal paper having a width of A4 size as a recording paper, and has a housing 3 having a substantially rectangular parallelepiped shape. The housing 3 accommodates a control circuit, a drive circuit, a drive motor, a thermal line head, a platen, and the like.

A cover 2 is provided on the housing 3. The cover 2 is located at two places 2X, 2 on the upper surface of the housing.
It is rotatably supported by X. Cover 2 with a solid line in Fig. 1
Shows a state in which the cover 2 is closed and a state in which the cover 2 is opened by a two-dot chain line. The recording paper P is introduced into the printer 1 from the recording paper insertion port 4 formed between the support portions 2X and 2X of the cover 2 between the cover 2 and the upper surface of the housing, and image formation is performed. The recording paper P introduced into the printer 1 is discharged from the recording paper discharge port 5 formed between the cover 2 and the front surface of the housing.

The cover 2 is provided with indicators (LEDs) 7, 8 and 9 which indicate the operating state of the printer 1. The display 7 indicates whether the power is on or off and whether an error has occurred. The display 8 indicates whether the data can be received. The display 9 displays information about the built-in battery.

A power switch 6 is provided on the upper surface of the housing 3. In the printer 1 of the present embodiment, operation modes such as power-on / off of the printer 1 and refreshing / charging of the built-in battery are switched according to the operation method (operation time / number of times) of the power switch 6. Has become. CPU10 is a port
Power switch 6 by the signal SW input to Port 8
Detect the operation state of.

FIG. 2 is a block diagram for explaining the control of the printer 1 of this embodiment. A 1-chip CPU 10 having an address space of 16 megabytes is used as a CPU (central processing unit) for controlling driving of the printer 1. The CPU 10 has address ports AB0 to AB23 and
EPROM21, D through data ports DB0-DB15
It is connected to the RAM 22, the font ROM 23, and the G / A (gate array) 26. The CPU 10 sends out address data designating an address to the address bus AB via the address ports AB0 to AB23, and the data port
Data is transmitted and received from the data bus DB via DB0 to DB15.

A program for controlling the driving of the printer 1 and various initial data are written in the EPROM 21. The DRAM 22 is a dynamic RAM used as an area for expanding a bitmap for image output based on print data transferred from the host computer or the like to the printer 1, an area for storing data from the interface, and a work area for other various processes. Is. Font ROM
A character font data 76 used for expanding the print data into a bit map on the DRAM 74 is stored.

The CPU 10 also includes a gate array (G /
A) Data exchange with the interface (I / F) 27, driving of the LEDs 7, 8 and 9 are performed via the A) 26. An interface (I / F) 27 is a printer interface (conforming to Centronics specifications) for receiving print data transferred from a host computer or the like, and has eight data lines and three control lines. . The eight data lines PDATA1 to PDATA8 are used to transfer print data from the host computer, and the three control lines are signals for causing the printer to read the print data.
(/ DATASTB), a signal indicating that the printer cannot receive the data (BUSY), and a signal indicating that the printer has read the data (ACK), respectively. In this specification, a low-active signal and a port that receives the low-active signal are indicated by "/" before the character string representing the signal or the port.

At the analog port AN2 of the CPU 10,
The partial voltage V_Batt of the battery voltage (or external power supply voltage) is applied. The CPU 10 detects the battery voltage (external power supply voltage) based on the A / D conversion value of the voltage value applied to the port AN2.

When the detected power supply voltage falls below a certain value, the reset IC 24 sends a reset signal (/ RESET) to CP.
Output to U10 port / RESET. When receiving the reset signal, the CPU 10 stops the operation. Therefore, when the power supply voltage becomes equal to or lower than the predetermined voltage value, the printing operation is stopped.

The cover 2 is provided with a paper sensor 25, and the output signal of the paper sensor is transmitted to the port PT of the CPU 10.
Input to OP. The paper sensor 25 is arranged so as to face the paper transport path with the cover 2 closed, and detects the presence or absence of recording paper in the paper transport path. When the cover 2 is open, the paper sensor 25 does not always detect the paper. Therefore, by monitoring the output signal of the sensor 25, it is possible to know whether or not the recording paper is set and the image forming operation is possible.

Xtal 15 is a reference clock generation circuit. The print data is bit-expanded in the DRAM 22 based on the reference clock generated by the Xtal 15. D
The data on the RAM 22 is transferred to the gate array 26,
Further, in synchronization with the transfer clock CLK, the divided print data DATA1 and DATA2 are transferred to the thermal head 40.

The heating energy of the heating resistor (not shown) of the thermal head 40 is the same as Port1 of the CPU 10.
~ Controlled by strobe signal sent from Port4 (details will be described later). In other words, the print data DA
The heating resistor to be driven is specified by TA1 and DATA2, and the heating resistor is driven to generate energy required for image formation by the strobe signal applied after the transfer of the print data.

The thermal head 40 is provided with a thermistor 41 for temperature detection. The output voltage of the thermistor 41 is applied to the analog input port AN1 of the CPU 10. CPU10 is the applied value (analog value)
The temperature of the thermal head 40 is detected based on the A / D converted value of

The CPU 10 has ports A // A / B // B
Sends a drive control signal for controlling the drive of the motor 134 to the motor drive circuit 430. The motor drive will be described in detail later.

The port PON1 is an F switch element.
It sends a signal to turn on / off the ET51. The port PON2 turns on the FET 52 as a switching element.
Send a signal to turn it off. An external power source (AC
When the adapter is connected, the transistor 53 as a switch element is turned on, and the signal /ADPT.IN input to the port Port7 becomes "L". CPU10 is / A
Based on the level of DPT.IN, the FET 52 is turned off when the external power supply is connected. However, if the refresh is performed even if the external power supply is connected, FE
T51 turns off and FET52 turns on. When the power switch 6 is turned on, the FET 51 or the FET 52 is turned on, and the DC-DC converter 50 converts the power supply voltage to supply power to the thermal head 40, the motor drive circuit 31, and the peripheral circuits. The DC-DC converter 50 further includes a CPU 10 and an EPROM 2
1, drive power supply Vcc (5
(Volts) are also output.

Note that once both FET51 and FET52 are turned off by the signals PON1 and PON2, DC-
Power is not supplied to the DC converter 50, and the CPU
The drive voltage Vcc is not supplied to 10. Therefore, F
When the ETs 51 and 52 are turned off, the power switch 6 is operated again to restart.

The printer 1 has a built-in nickel-cadmium battery 100 as a driving power source.
You have a voltage of 4.4 volts. Further, the printer 1 of this embodiment is provided with a power supply connector 70, and an AC adapter 80 can be connected thereto. AC adapter 80
Has a constant current circuit 81 in addition to the constant voltage circuit 82 for supplying the drive voltage of the printer 1. The constant voltage circuit 82 is DC-via the connector 70 and the FET 51.
It is connected to a DC converter. The constant current circuit 81 is connected to the charging control circuit 60 via the connector 70.

The printer 1 of this embodiment is controlled by the printer 1 so that the constant current circuit 81 inside the AC adapter 80 is controlled.
The built-in battery is charged using the current output by. By providing the constant current circuit 81, which is required only during charging, on the AC adapter 80 side instead of the printer 1 main body, the printer 1 can be made lighter and more compact.

The printer 1 according to the present embodiment refreshes the built-in battery (nickel-cadmium battery) 100.
Has a charging function. The charge control circuit 60 performs the refresh / charge control of the built-in battery 100. C
When the / CHARGE signal is output from the Port 5 of the PU 10 to the charge control circuit 60, the charge control circuit 60 starts charging the battery 100 with the current from the constant current circuit 81. The charging is finished by monitoring the voltage of the battery 100.

When refresh is performed, CP
The / REFRESH signal is output from Port 6 of U10, and the current from the constant current circuit 81 is not applied to the battery 100. Further, although the AC adapter 80 is connected, the FET 51 is turned off, the FET 52 is turned on, and the battery 100 is refreshed.

The thermal head 40 of the printer of this embodiment
Is a line thermal head in which heating resistors of 2560 dots (2560 pieces) are arranged in a horizontal row. 1st to 12th
80th dot data (data indicating ON / OFF)
Is sent to the thermal head 40 from the CPU 70 as DATA1 and the 1281st to 2560th dot data as DATA2. Note that, as described above, the dot data sent to the thermal head 40 is sent as serial data in synchronization with the transfer clock CLK.

For printing on thermal paper, 2560 heat generating resistors are divided into four blocks, first to fourth blocks, which are driven and controlled by strobe signals / STB1 to / STB4, and the timing is shifted by 2 blocks. (2 split drive). The four blocks of heating resistors are strobe signals.
By setting / STB1 to / STB4 to "L", electricity is generated and heat is generated according to the print data (dot data). It should be noted that this blocking is performed in order to prevent a large amount of current from flowing at one time and draining the battery. Therefore, all four blocks can be driven at the same time when the battery is fully charged or when the power consumption is not a problem such as when an external power source is connected.

FIG. 3 is a conceptual diagram showing the structure of the thermal line head 40. 1st to 1280 as described above
The data corresponding to the 40th heating resistor 40H is the CPU
When the data is transferred from 10, the data is stored in the shift register 40A provided in the thermal line head 40 in synchronization with the transfer clock CLK. There is a one-to-one correspondence between the heating resistor 40H of the thermal head and each bit of the shift registers 40A and 40B. If the content of the shift register is "1" / STBn (n = 1,2,3,4) Becomes "L", the corresponding heating resistors of the first to fourth blocks generate heat.

FIG. 4 is a timing chart showing how the data DATA1 and DATA2 are transferred and the thermal head 40 and the drive motor 32 are controlled.

When the bit map is developed on the DRAM 74, one line of print data is transferred from the gate array 26 to the thermal head 40. As mentioned above, first, D
ATA1 (data corresponding to the first to 1280th heating resistors) is transferred in synchronization with CLK.

When the transfer of DATA1 is completed, the motor 3
2 is started to start the conveyance of the paper, and at the same time, / STB1 and / STB2
Is set to "L", and the heating resistors (1
Drive up to 1280th). Further, when / STB1 becomes "L", the contents of the shift register A cannot be rewritten even if data is written in the shift register B. When / STB1 and / STB2 become "L", DATA2 is promptly changed.
Transfer is started. That is, DATA2 (data corresponding to the 1281st to 2560th heating resistors) is synchronized with CLK while driving the 1st to 1280th heating resistors (first and second blocks). Forward. / S
DAT is already available when the drive by TB1, / STB2 is completed.
Since the transfer of A2 is also completed, next set / STB3 and / STB4 to "
L "to drive the third and fourth block heating resistors (1281st to 2569th heating resistors). By thus setting / STB1 to / STB4 to" L "for a predetermined time, the thermal line The driving of the heating resistors in one row of the head is completed (the image formation for one row is completed).

In FIG. 4, by setting / STB1 and / STB2 to "L" for the time T, the first heating resistor is 128.
Up to 0th drive, / STB3, / STB4 is "L" during time T
By doing so, the 1281st to 2560th heating resistors are driven. Similarly, print the second line with / S
This is executed by setting TB1 and / STB2 to time T 1, and then setting / STB3 and / STB4 to "L" for time T 2.

As shown in the figure, the motor drive pulses A./A.B./B shift to the next pattern when the driving of the heating resistors of the first and second blocks by / STB1 and / STB2 is completed. That is, while the first to 1280th heating resistors (first and second blocks) are being driven, A = "H", /
The pattern is A = "L", B = "L", / B = "H", and 128
While the first to 2560th heating resistors (third and fourth blocks) are being driven, A = "H", / A = "L", B = "H",
The pattern is / B = "L". Thereafter, the excitation pattern is updated each time two blocks of the heating resistor divided into four are driven in the same manner. In this printer, when a drive pulse of one pulse (one pattern) is applied to the drive motor 32, the paper advances by ½ line. That is, when a drive pulse of 2 pulses is applied to the drive motor 32, the paper is conveyed by one line, and all the heating resistors are driven during that time. In this way, 1 sheet of paper
The printing of one page is completed by repeating the process of carrying one line and printing one line in the meantime.

In the printer 1 of this embodiment, the following drive control is performed in order to remove the influence of sticking on the formed image. When the printing rate (= the number of heating resistors driven to generate heat for printing / the total number of heating resistors) is low, the normal two-division drive control described above is performed. In the present embodiment, the print rate is defined as the number of 1s (on) in the print data of the registers 40A and 40B divided by the number of bits of the data. When the printing rate is high, when the normal two-division driving is performed, the line printed by the sticking apparently becomes dark. For this reason, when the printing rate is high, the four-division driving in which the timings of the four strobe signals are shifted is adopted to prevent the occurrence of sticking and prevent the print line from becoming dark.

FIG. 5 is a flowchart for determining the strobe timing for each of the first to fourth blocks. Here, the first block and the second block are combined to form a first group, and the third block and the fourth block are combined to form a second group, and two blocks are driven simultaneously or sequentially in each group. Has been decided. First, the first group (first block and second group
The printing rate of the block) (the number of heat generating resistors driven by heat generation / the total number of heat generating resistors in the group) is determined (S1). When the print ratio is larger than the predetermined value x (Y: S3), the first
The two blocks in the group are divided and driven. That is, by shifting the timing of / STB1 and / STB2 when driving the heating elements of the first group (1st to 1280th heating resistors), the first block and the second block included in the 1st group Is divided into two (S7), and the driving is performed by shifting the timing. Although the flow chart shows only the processing for one group, when the second group (the heating elements from the 1281st to 2560th heating elements) is driven, similarly, when the printing rate is high. By shifting the timing of / STB3 and / STB4 for the 3rd and 4th blocks in the group,
Drive at different timing. By controlling in this manner, when printing one line, the heating resistors are divided into 2 to 4 blocks and driven according to the printing rate, so the adverse effect of sticking can be eliminated. When the print ratio is less than or equal to the predetermined value x (N: S3), the two blocks in the group are not divided and are driven simultaneously (S5).

FIG. 6 is a flow chart showing a simplified control as the second embodiment. In the second embodiment, the total number of heating resistors is set to 2 based on the printing rate of one line.
It is divided into one or four blocks. In S10,
The printing rate is determined based on the total number of heating resistors and the number of resistors driven to generate heat for forming one line of image. It is determined whether the print ratio exceeds a predetermined value x (S1
1) If the value is larger than the predetermined value x, all heating resistors are divided into four blocks. If the print ratio is less than or equal to the predetermined value x, all the heating resistors are divided into two blocks. The blocks thus divided are driven at different timings.

FIG. 7 is a timing chart showing the timing of the strobe signal in the case where all the heating resistors are divided into four blocks, that is, the first block to the fourth block and driven.

When the transfer of DATA1 is completed, the motor 3
2 is started to start the conveyance of the paper, and at the same time, / STB1 and / STB2
To "L" in order, and the heating resistors (1
(The 1280th) is sequentially driven. / STB2 is "L" for / STB1
From "H" to "L" immediately. Also, / STB1 is "
When it goes to L ", DATA2 is immediately transferred./STB2
Since the transfer of DATA2 has already been completed by the time when the driving by, the / STB2 and / STB3 and / STB4 are sequentially set to "L", and the heating resistors of the third and fourth blocks (heating resistance The 1281st to 2569th bodies are sequentially driven. By setting / STB1 to / STB4 to "L" for each predetermined time T in this manner, the four-division driving of the heating resistors in one row of the thermal line head is completed (image formation for one row is completed). FIG. 7 shows a state of image formation for two lines,
In each row, the heating resistor is divided into four blocks and driven. In Figure 7, / STB1 and then /
By setting STB2 to "L" for time T, 1
The driving from the 1st to 1280th is completed, and / STB3 and then / STB4 are set to "L" for the time T, so that 128
The driving of the first to 2560th heating resistors is completed. Similarly, the second line is printed every T times / STB1 to / STB4
Are sequentially set to "L" for execution.

The motor drive pulses A // A / B // B are used to drive the heating resistors by / STB1 and / STB2 as shown in the figure.
Every time the drive by / STB3 and / STB4 ends, that is, 1 /
Each time printing of two lines is completed, the pattern moves to the next pattern, and the recording paper is conveyed by 1/2 line.

Although the above embodiment is a printer for recording on thermal paper by using a thermal line head, the present invention uses the thermal line head to transfer the ink of the thermal ink sheet to plain paper. It is also applicable to various printers.

In the above embodiment, the print ratio is set as the total number of heat generating resistors / heat generating resistors driven to generate heat, and control is performed according to the size of the print ratio. However, the present invention is not limited to the control by comparing the print ratios,
For example, the same effect can be obtained by comparing the reference value with the number of heat generating resistors that are driven to generate heat and performing control according to the magnitude relationship.

[0043]

As described above, according to the thermal head driving method and apparatus of the present invention, the drive of the heating resistor is divided into blocks and controlled, and usually the number of divisions is made small and the printing rate is high. Since the number of divisions is increased and printing is performed by shifting the driving timing of each block, the effect of sticking can be effectively suppressed.

[Brief description of drawings]

FIG. 1 is a perspective view showing the external appearance of a thermal line head printer that is an embodiment of the present invention.

FIG. 2 is a block diagram for explaining control of a thermal line head printer.

FIG. 3 is a diagram showing a configuration of a thermal head.

FIG. 4 is a timing chart for explaining print control.

FIG. 5 is a flowchart illustrating print control according to an embodiment of the present invention.

FIG. 6 is a flowchart illustrating print control according to the second embodiment of the present invention.

FIG. 7 is a timing chart in the case where the heating resistor is divided into four blocks and the driving is performed with a shifted timing.

[Explanation of symbols]

 1 Printer 2 Cover 3 Housing 10 CPU 40 Thermal Head

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Mikio Horie 2-36-9 Maeno-cho, Itabashi-ku, Tokyo Asahi Kogaku Kogyo Co., Ltd. (72) Inventor Hiroshi Oda 2-36-9 Maeno-cho, Itabashi-ku, Tokyo No. Asahi Kogaku Kogyo Co., Ltd. (72) Inventor Katsuka Suzuki 2-36 Maeno-cho, Itabashi-ku, Tokyo No. 36 Asahi Kogaku Kogyo Co., Ltd.

Claims (3)

[Claims] 1. A printer for forming an image on a recording sheet by using a thermal line head having a plurality of heating resistors arranged linearly, wherein the plurality of heating resistors are divided into a plurality of blocks. Driving means capable of independently driving heat generation for each block, printing rate determining means for determining a printing rate based on print data input to a thermal head, and printing rate determined by the printing rate determining means In response to the,
A timing determining unit that determines a timing for driving the plurality of blocks to generate heat,
Thermal head drive device. 2. A printer for forming an image on a recording sheet using a thermal line head having a plurality of heating resistors arranged linearly, wherein the heating resistors are driven to generate heat at the same time. Dividing means for dividing into a plurality of blocks for each, driving means for driving the plurality of blocks at different timings, printing rate determining means for determining a printing rate based on print data input to a thermal head, and the dividing means A thermal head driving device, comprising: a control unit configured to change the number of blocks divided by the unit according to the printing rate determined by the printing rate determining unit. 3. A printer for forming an image on a recording sheet by using a thermal line head having a plurality of heating resistors arranged in a line, wherein the printing rate is determined based on print data input to the thermal head. A method of driving a thermal head, characterized in that the plurality of heating resistors are divided into a plurality of blocks according to the printing rate, and the plurality of divided blocks are driven at different timings.