JPS61189961A - Method for driving thermal head - Google Patents

Abstract

PURPOSE:To provide a thermal head driving method capable of sufficiently reducing the generation of noise and the variation in the voltage of a power source, by controlling the generation of the pulses respectively applied to heat generators by generating applying pulses in a timewise overlapped state so that timewise almost central positions coincide to each other. CONSTITUTION:Applying pulses are generated in a state timewise overlapeed with respect to unit heat generators so that timewise almost central positions thereof coincide to each other to control the generation of pulses respectively applied to heat generators. When a thermal head driving method was taken, the applying pulses are generated in such a state that times T1, T2 respectively almost correspond to the central positions of the applying pulses. As a result, the total current I required by a thermal head changes with respect to an elapsed time t1 as shown by Fig. A and the output voltage V of a power source gently varies as shown by Fig. B. That is, as the result of the timewise dispersion of a current beginning to flow in each unit heat generator, the abrupt variation of the current consumed by the whole of the thermal head is prevented and the output voltage of a power source can be stabilized and the reduction in the generation of noise can be attained.

Description

[Detailed description of the invention] "Industrial application field" The present invention relates to a method for driving a thermal head.

"Prior art" One or more heating elements (heating elements) are arranged in a one-dimensional or two-dimensional
The thermal head, which is arranged dimensionally, generates heating elements as units (hereinafter referred to as unit heating elements) according to image information.
can be selectively heated. The heat pulses thus generated are used to record an image in a thermal recording device or a thermal transfer recording device, and are used to form a magnetized latent image in some types of display devices.

By the way, since recording devices and display devices using thermal heads perform recording or display (hereinafter simply referred to as recording) using thermal energy, the energy applied to each unit heating element is the optical power of each pixel. Affects concentration.

Therefore, control is performed to vary the applied energy for each unit heating element, not only when expressing gradation, but also when correcting the heat accumulation phenomenon of the thermal head.

FIG. 4 schematically shows, by way of example, a thermal head driving device for correcting the heat accumulation phenomenon. Thermal head driving methods and driving devices for correcting the heat accumulation phenomenon have been disclosed in many applications such as Japanese Patent Application No. 58-55265.

Incidentally, the buffer memory 11 of this apparatus is supplied with an image signal 12 obtained by plane-scanning a document (not shown). The buffer memory 11 is a memory that sequentially stores image signals for three lines, for example, and stores pixels (hereinafter referred to as reference dots) located around a pixel (hereinafter referred to as a dot of interest) whose applied energy is currently being calculated. The signal state 13 is output to the first arithmetic unit 14.

As shown in FIG. 5, the dot 15 of interest is M on the Nth line.
If it is the pixel of M-1 and M of the same line,
+1st dot and M-1 to M+1st dots on N-1 line one line before, and N one line before
The Mth dot in the -2 line is used as a reference dot, for example. The first arithmetic unit 14 weights these six reference dots according to the contribution rate of heat storage, and adds the weights of the dots to be printed among them. In this way, the heat storage contribution rate of the surrounding dots to the dot of interest is calculated. The weighting is, for example, as shown in FIG.

The heat storage calculation result 16 is supplied to a second calculation unit 17 . The second calculator 17 calculates the energization time of the applied pulse used to print the dot of interest, depending on the amount of heat storage. At this time, other data 18 such as the energization time of the applied pulse used in the previous line may be supplied to the second arithmetic unit 17 to correct the applied pulse width. The applied pulse width information 19 determined by the second arithmetic unit 17 is supplied to the recording section (or display section) 21, and the applied pulse width for recording the image signal 22 supplied from the buffer memory 11 is set. .

That is, in the recording section 21, the applied pulse width is set for each unit heating element, for example, in steps of 0.1 m5ec. When heat storage is progressing, the applied pulse width is set to be short depending on the degree of heat storage.

FIG. 6 shows an example of applied pulses. The applied pulse 23 is thus applied at predetermined times t1, t2...
... to each unit heating element R1, R2, ...... -
applied simultaneously. Therefore, if the total current flowing through the thermal head is 1 and the elapsed time is t, the amount of current required by the thermal head initially reaches the maximum value at once, as shown in Figure 7 (A), and then gradually. It will be like this.

``Problems to be Solved by the Invention'' For this reason, the current flowing to the thermal head increases rapidly at the start of energization, which may generate noise and adversely affect logic circuits and the like.

In addition, as shown in Figure (B) compared to Figure (A), the output voltage of the thermal head's power supply circuit fluctuates greatly, and unless a new power supply voltage compensation circuit is installed, each unit heating element will A problem arose in that the desired energy was not supplied.

In view of these circumstances, the present invention provides a thermal head driving method that can sufficiently reduce noise generation and power supply voltage fluctuations in a recording device or a display device that controls the energy of each unit heating element based on the time width of the applied pulse. Its purpose is to provide.

"Means for Solving the Problem" In the present invention, applied pulses that are generated temporally overlappingly to each unit heating element are applied to each heating element so that their temporally approximately central positions coincide with each other. Controls the generation of applied pulses applied to the

FIG. 1 shows an example of how applied pulses are generated when the thermal head driving method of the present invention is used, and corresponds to FIG. 6. Time T1, T2 in the figure...
... corresponds approximately to the center position of each applied pulse 23. As a result, the total current ■ required by the thermal head changes as shown in Figure 2 (A) with respect to the elapsed time t, and the output voltage ■ of the power supply circuit changes as shown in Figure 2 (B). The fluctuation is gentler than in FIG. 7(B). That is, the current that starts flowing into each unit heating element is dispersed over time, so that the current consumed by the entire thermal head does not fluctuate rapidly. In this way, it is possible to stabilize the output voltage of the power supply and reduce noise generation.

"Example" The present invention will be described in detail below with reference to Examples.

FIG. 3 shows the main parts of a recording apparatus using the thermal head driving method of the present invention. The same parts as in FIG. 4 are given the same reference numerals.

Now, an image signal 12 is supplied to the buffer memory 11 of this device in synchronization with a video clock 32 supplied from a timing control circuit 31. The buffer memory 11 outputs the signal state 13 of the reference dot with respect to the dot of interest,
Based on this, the applied pulse calculation circuit 33 calculates the heat storage state of the unit heating element corresponding to the dot of interest.

The applied pulse calculation circuit 33 is a circuit in which the first edict and the second calculation unit 14.17 shown in FIG. Output to ROM34.

The pulse waveform ROM 34 uses the applied pulse width information 19 as address information and reads out the generation timing and time width of the applied pulse in the form of decomposed unit pulse information 35 for each printing cycle. Here, the printing cycle refers to a cycle in which unit-length pulses (hereinafter referred to as unit pulses) constituting the applied pulse are printed. Assuming that this cycle is set to 0.1 mS in this example,
The applied pulse of 1 ms is composed of 8 unit pulses,
The applied pulse of 0.8 mS is composed of eight unit pulses.

Now, the time width of the applied pulse applied to each unit heating element is 0.
．． If it is set in 8 steps between 5 and 1.2 mS, the relationship between the applied pulse width information 19 and the unit pulse information 35 will be as shown in Table 1 below.

However, in this table, information “1” indicates the state where there is a unit pulse.
Further, information "0" represents a state in which there is no unit pulse.

The unit pulse information 35 is supplied to the transfer/transmission signal buffer 36 as information of 8 bits each, and is written into the eight address areas A1 to A8 in a state of 1 bit each under the control of the address control circuit 37. Each address area A1 to A8 has a bit capacity corresponding to the total number of pixels of l line, and when the unit pulse information 35 is outputted for all the pixels of l line, the transfer signal buffer 36 is stored for l line. Writing of all pulse information is completed. However, since the 8-bit unit pulse information 35 is information assuming that the dot of interest is a printed dot (black dot), when the image signal 39 of the dot of interest corresponds to a non-printed dot (white dot), the unit pulse information 35 is Regardless of the content of the information 35, all "0" information is written into corresponding positions in each of the address areas A1 to A8.

When all the pulse information for one line has been written into the transfer signal buffer 36 in this way, the information in the first address area A1 is first read out under the control of the address control circuit 37, and the information is read out from the thermal head as cycle image data 41. 42. This cycle image data 41 is set in a shift register (not shown) mounted on the thermal head 42, and is further latched by a latch circuit (not shown), after which energization control of each unit heating element is performed. At this time, information “1” constituting the cycle image data 41
0.1 mS is applied to the part of the unit heat generating element corresponding to the information "0", and no current is applied to the part of the unit heat generating element corresponding to the information "0".

While the first energization control is being performed, the information in the second address area A2 is set in the shift register of the thermal head 41. Then, at the same time as the first energization control ends, a second energization control is performed based on the information in the second address area A2. After the energization control is performed eight times in the same manner, the printing operation for one line is completed.

At the same time, the timing control circuit 31 sends a sub-scanning control signal 45 to the motor driver 44, and the step motor 46
is driven by a predetermined amount. As a result, the drive roller 47 rotates by a predetermined angle, and the recording paper 48 is sub-scanned by one line. Thereafter, the next line is printed by the same operation as already described. Recording will proceed in the same manner thereafter.

In this recording device, as is clear from Table 1, the generation of applied pulses to each unit heating element is controlled with the 4th and 5th print cycles corresponding to the 4th and 5th address areas as the center of the time axis. be done.

In other words, this reduces noise generation and reduces the burden on the power supply.

Note that, as shown in this example, the precision of matching the applied pulse with respect to the temporal center position does not necessarily have to be exact, and even if an error of several tens of percent occurs, it is sufficient for practical use. effect can be obtained. Furthermore, although the embodiment has been described on the assumption that one line of unit pulses are generated sequentially in time, it is also possible that a certain amount of time gap exists between them.

"Effects of the Invention" As explained above, according to the present invention, sudden fluctuations in current can be avoided not only when the current flows into the thermal head when it is turned on but also when it is turned off. Even when compared with a thermal head driving method in which energization is controlled by matching the trailing ends of pulses, it is possible to similarly reduce noise and stabilize the power supply. Therefore, by using the thermal head driving method of the present invention, it is possible to reduce the cost required for noise countermeasures, power supply stabilization measures, etc., and it is also possible to obtain a recording surface or display image with more uniform image quality.

[Brief Description of the Drawings] Figure 1 is a waveform diagram showing an example of the applied pulses applied to each unit heating element when the multi-head driving method of the present invention is used, and Figure 2 (A) is a waveform diagram of the present invention. A diagram showing an example of a temporally required value of the total current consumption of the thermal head in the invention,
Figure 4 (B) is a characteristic diagram showing an example of changes in the output voltage of the power supply in this case, Figure 3 is a block diagram showing the main parts of the recording device to which the present invention is applied, and Figure 4 is a conventional thermal head drive. A block diagram of a thermal head according to the method, FIG. 5 is an explanatory diagram showing the relationship between a dot of interest and a reference dot, and FIG. 6 shows an example of the applied pulse applied to each unit heating element by the conventional thermal head driving method. Waveform diagram, Figure 7 (
A) is a diagram showing an example of the temporally required value of the total current consumption of a conventional thermal head, and FIG. 34...Pulse waveform ROM. 37... Transfer signal buffer, 41... Cycle image data, 42... Thermal head. Applicant: Fuji Xerox Co., Ltd. Representative
Person Patent Attorney Ume Yutomi Yamauchi 2
Figure 4 Figure 5 Figure 7; 1

Claims (1)

[Claims] In a device that can perform thermal recording or display with different energies by supplying application pulses with different time widths to multiple heating elements that make up a thermal head, application that occurs overlappingly in time A method for driving a thermal head, comprising: controlling the generation of applied pulses applied to each heating element such that the temporally central positions of the pulses coincide with each other.