JPH07125294A - Multi-gradation image data printing method for thermal head - Google Patents

Abstract

PURPOSE:To print multi-gradation image of high image quality by preventing generation of white striping of a block boundary, density unevenness of printing, etc. CONSTITUTION:A thermal head 4 is driven by intermittently alternately continuing a strobe A and a strobe B by strobe signal generating means 9 based on a unit pulse from unit pulse generating means 5 at a period of a unit pulse for a first gradation value until predetermined number of pulses are counted up by preliminarily heating pulse counting means 6. After a second gradation value, the strobes A, B are active to be sequentially divided to be driven at a thermal head 4 by the means 9 based on control of gradation time control means 9 referred with a conducting time of conducting time memory means 7, and printed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voltage applied to a line head according to density information of a pixel corresponding to multi-gradation image data for each heating resistor of a line head having a plurality of heating resistors. The present invention relates to a method of printing multi-gradation image data by a thermal head, which performs time control and performs dot recording with a density according to the energy supplied to a heating resistor based on this control.

[0002]

2. Description of the Related Art In a thermal printer or the like, a voltage is simultaneously applied to all heating resistors included in a line head, and a voltage is applied to each heating resistor according to density information of pixels corresponding to each heating resistor. Performing the time control of causes a decrease in the output voltage of the power supply for driving the head and causes density unevenness in the printed image.
The heating resistor is divided into a plurality of blocks (block A, block B in FIG. 2) by a well-known drive circuit configuration as shown in FIG. 2, which is also used as a part of the configuration of an embodiment of the present invention described later. Then driven. As a method of controlling the voltage application time to the heating resistor at that time, as shown in FIG. 6 as a first conventional example, first, head drive (voltage application) is performed on the heating resistor of the first block A. Signal is activated (High level), and the strobe B signal is activated so that the voltage is applied to the second block B after the voltage application to the block A is completed.

As a second conventional example, as shown in FIG. 7, strobe A and strobe B are arranged so that voltage application is alternately repeated between blocks for each gradation within one line printing time.
Some control the signal. Further, as a third conventional example, as shown in FIG. 8, the strobe A and strobe B signals are controlled so as to switch the voltage application between the blocks for each reference time by using a unit pulse within the printing time of one line. There is.

[0004]

However, as in the first conventional example, the drive of each block is completely shifted to apply a voltage to the head (for strobe A for block A and for block B). Strobe B) and residual heat from the adjacent heating resistors at the block boundary cannot be obtained, so that white stripes are generated at the boundary between the blocks, and the sub-scanning is performed between the blocks due to the time difference in the energization between the blocks. There was a problem that print misalignment occurred in the direction. Further, in the second conventional example, in order to solve the problem of the first conventional example, the drive between blocks is switched for each gradation within the printing time of one line. As described above, since the heating time of the first gradation is generally longer than the heating time of other gradations (second gradation and thereafter) because preheating (preheating) is required, the first gradation of block A is ~ Waiting time t1 between second gradations
Since the waiting time t2 between the first gradation and the second gradation of the block B is greatly different, there is a problem that a difference occurs in heat timing between the blocks and a density difference appears in printing. Further, in order to solve the problem of the second conventional example, the third conventional example adopts a so-called chopper system in which the drive of each block is alternately switched within the printing time of one line at the reference time. Since the accuracy can be obtained by shortening the cycle of the unit pulse to be counted in order to perform the gradation vs. density characteristic strictly, if the cycle is shortened, the current characteristic of the heating resistor load deteriorates and density unevenness occurs. There was a problem of being lost.

[0005]

In order to solve the above problems, the present invention stores multi-tone image data composed of inputted first to nth tones in a storage means. A step of expanding the gradation data of the multi-gradation image data stored in the storage means in association with a plurality of heating resistor elements of the thermal head, and the expansion data expanded in the gradation expansion step. According to the step of energizing the heating resistor element for each block in a time-divisional manner, the method of printing on a recording paper, the energizing period according to the expanded first gradation data in the energizing step A method for printing multi-gradation image data by a thermal head, characterized in that energization to the heating resistor element is repeatedly turned on / off a plurality of times within a time width shorter than the period.

[0006]

By performing the multi-gradation image data printing method as described above, the preheating of the thermal head can be uniformly performed between blocks in time, and the gradation reproducibility becomes good, and the power consumption is reduced. It is possible to perform high-quality printing in which white stripes do not occur at block boundaries and density unevenness does not occur even though the block division driving is suppressed.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described with reference to FIGS. First, the gradation control means for printing a multi-gradation image of the present invention will be described based on the block diagram of FIG.
Reference numeral 1 denotes a multi-tone image data input means for inputting multi-tone image data given from the outside, which is composed of an interface circuit or the like. 2 is a storage means for storing the multi-tone image data from the multi-tone image data input means,
It is composed of RAM. Reference numeral 3 is a gradation developing means for expanding the multi-tone image data in the storage means 2 into binary gradation developing data for each line, which is constituted by a RAM and is expanded by a program. A thermal head 4 is composed of a plurality of heating resistors. Reference numeral 5 is a unit pulse generating means that serves as a drive control signal source when the thermal head 4 is preheated, and is usually constituted by an astable multivibrator or a time base collector for dividing the output signal of the crystal oscillator. Reference numeral 6 is a preheating pulse counting means for counting the number of output pulses from the unit pulse generating means 5 by a predetermined number, by a shift register which normally generates a carry signal, or a cascade connection of several JK flip-flops. Composed. Reference numeral 7 denotes an energization time storage means for storing energization time data for each gradation corresponding to the print density, which is usually constituted by a ROM. Reference numeral 8 is a gradation time control means for controlling the energization pulse width to the heating resistor element of the thermal head 4 by referring to the energization time data of the energization time storage means 7, a retrigger one-shot monostable multivibrator, or It is composed of a time base collector. 9 is the thermal head 4
Is a strobe signal generating means for generating a strobe signal to be given to, and is usually constituted by a bistable multivibrator or the like. Reference numeral 10 is a print data transfer means for transferring the multi-gradation image data stored in the storage means 2 to the binary development data in the form of binary matrix by the gradation development means 3 and transferring it to the thermal head 4. Yes, normal RAM
It is composed of Reference numeral 11 denotes a CPU that controls the above-mentioned means and controls them so as to be associated with each other.

Next, the structure of the thermal head shown in FIG. 2 will be described. Reference numeral 21 is a shift register that serially takes in the binary print image data from the print data transfer means 10 bit by bit in accordance with a clock, and 22 is a parallel register that takes in the print image data in the shift register 21 by a latch signal and holds it. It is a latch circuit that Reference numeral 23 is a gate circuit for taking a logical product of each parallel output signal of the latch circuit 22 and a strobe signal, and 24 is conductive according to each output of the gate circuit 23,
The drive circuit is composed of a power transistor that is non-conductive. Reference numeral 25 is a heating resistor element group of the thermal head that is independently driven by the drive circuit 24.

Next, the operation of the gradation control means will be described with reference to FIG.
It will be described with reference to FIG. The multi-tone image data (STEP1) input from the outside is stored and stored in the storage means 2 (STEP2). Now, assuming that the expressed gradation value is 64 and the resolution of the thermal head is 256 per line, the multi-gradation image data in this storage means is 2 of 0 and 1 in 63 rows and 256 columns.
The gradation developing means 3 for expanding the gradation into the value data develops the gradation as shown in FIG. 3 (STEP 3). The gradation-developed image data is sequentially input from the first gradation value to the 64th gradation value to the shift register 21 at the timing of the clock signal by the print data transfer means 10 and then the latch circuit 22 by the latch signal. Is latched to (STEP 4). When the data latched in the latch circuit 22 has the first gradation value, the strobe signal generating means 9 time-divides strobe A and strobe B in a complementary manner according to the output of the unit pulse generating means 5. ON / OFF is repeated with a pulse of a predetermined cycle, and when the count-up signal of the predetermined pulse number of the preheating pulse counting means 6 is detected, this is stopped (STE).
P5).

Subsequently, the image data of the second gradation value latched by the latch circuit 22 via the shift register 21 (STEP 4) is supplied by the strobe signal generating means 9 to the second gradation of the energization time storing means 7. According to the control signal from the gradation time control means 8 referring to the energization time (for example, 5 ms), the strobe A is first turned on, and after the second gradation energization time (for example, 5 ms) has passed, it is turned off and the strobe B is turned on. Then, after the second gradation energization time (for example, 5 ms) has passed, this is turned off (STE
P5). Similarly, after the third gradation, the shift register 21 is also used.
The image data of each gradation equivalent period sequentially latched by the latch circuit 22 via (STEP 4) is sequentially turned on in the energization time storage means 7 according to the energization time (STEP 5), 63. The multi-gradation image for one line is repeated in the gradations of block A,
Printing is performed by driving the block B in two divisions. Above STE
Each of P2, STEP3 and STEP5 constitutes a step of storing the multi-tone image data in the storage means, a step of developing the tone of the multi-tone image data, and a step of time-dividing the developed data for each block.

As shown in the timing chart of the unit pulse of strobe A and strobe B as shown in FIG. 5, strobe A and strobe B are never turned on at the same time.
It is designed to be completely divided drive. In addition, the first grayscale value has a plurality of unit pulses repeated in both strobe A and strobe B, and there is no long pause period.
The cooling efficiency after heating of the thermal head is absorbed, the heating efficiency is good, and the heating is performed uniformly between the blocks, so that the total energization time can be shortened. Further, after the second gradation, the pulse width control is such that the energization time is controlled so that the print density is in accordance with each gradation, which is strict in consideration of the gradation vs. density characteristics.

In the above embodiment, the thermal head is block A.
Although the driving is performed by dividing into two blocks, that is, the block B, the driving is not limited to this and multi-division driving of three or more may be performed. At this time, the strobes corresponding to each block are controlled to be sequentially turned on so as to circulate between the blocks.

[0013]

According to the present invention, since the thermal head is divided and driven, it is advantageous in terms of power consumption, density unevenness due to a decrease in power supply voltage can be reduced, and drive switching between blocks is performed within one line. Therefore, there is no printing deviation between blocks in the sub-scanning direction. By repeating ON / OFF of the pulse evenly between blocks during the preheating period, white stripes do not occur even at the block boundaries, and the current characteristics with respect to the heating resistor load can be selected so that there is no density unevenness. This has the effect that good image printing can be performed.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention.

FIG. 2 is a circuit diagram of a thermal head according to an embodiment of the present invention.

FIG. 3 is a table showing an example of gradation development data according to an embodiment of the present invention.

FIG. 4 is a flowchart showing the operation of the embodiment of the present invention.

FIG. 5 is a timing diagram of a strobe signal according to an embodiment of the present invention.

FIG. 6 is a timing diagram of a strobe signal according to a first conventional example.

FIG. 7 is a timing diagram of a strobe signal according to a second conventional example.

FIG. 8 is a timing diagram of a strobe signal according to a third conventional example.

[Explanation of symbols]

 1 multi-gradation image data input means 2 storage means 3 gradation development means 4 thermal head 5 unit pulse generation means 6 preheating pulse counting means 7 energization time storage means 8 gradation time control means 9 strobe signal generation means 10 print data transfer Means 11 CPU STEP2 Step of storing multi-tone image data STEP3 Step of developing multi-tone image data STEP5 Step of time-division of developed data

Claims (1)

[Claims] 1. A step of storing, in a storage means, multi-tone image data composed of inputted first to n-th tones, and multi-tone image data stored in the storage means. In accordance with a plurality of heating resistor elements of the thermal head for gradation development, and the heating resistor elements are time-divided for each block according to the expansion data expanded in the gradation development step. In the method of printing on recording paper by the step of energizing, in the energizing step, the energizing period corresponding to the expanded first gradation data is shorter than the energizing period, A method for printing multi-gradation image data using a thermal head, which is characterized by repeating ON / OFF a plurality of times.