JPH0572267B2 - - Google Patents

Description

[Detailed description of the invention]

``Industrial Application Field'' The present invention relates to a method for driving a thermal head. ``Prior Art'' A thermal head is made up of one or more heat generating elements (heat generating elements) arranged one-dimensionally or two-dimensionally, and these heat generating elements (hereinafter referred to as unit heating elements) are arranged as units according to image information. . can be selectively heated. The heat pulse generated by this is
It is used in thermal recording devices or thermal transfer recording devices to record images, and in some types of display devices it is used to form magnetic latent images. 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 affects the optical density of each pixel. 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 drive device for correcting the heat accumulation phenomenon. The thermal head driving method and driving device for correcting the heat accumulation phenomenon are disclosed in the patent application filed in 1983-
It has been disclosed in many applications such as No. 55265. Incidentally, the buffer memory 11 of this apparatus is supplied with an image signal 12 obtained by plane-scanning an original (not shown). The buffer memory 11 is a memory that sequentially stores image signals for three lines, for example, and stores signals of pixels (hereinafter referred to as reference dots) located around the pixel (hereinafter referred to as the dot of interest) for which the current applied energy is to be calculated. Condition 13
is output to the first arithmetic unit 14. As shown in FIG. 5, if the target dot 15 is the M-th pixel on the N-th line, then the M-1 and M+1-th dots on the same line, and the M-1 pixel on the N-1 line one line before. The Mth dot on the N-2th line one line before the dot M+1 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 are stored in the second line.
The applied pulse width may be corrected by supplying it to the arithmetic unit 17. The applied pulse width information 19 determined by the second calculator 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. Ru. That is, in the recording section 21, for example,
Set the applied pulse width for each unit heating element in 0.1 msec increments. 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 a predetermined time t ₁ ,
From t _{2 .} . . , it is applied all at once to each unit heating element R1, R2, . For this reason, if the total current flowing through the thermal head is I and the elapsed time is t, the amount of current required by the thermal head will initially reach the maximum value at once, as shown in Figure 7A, and then gradually decrease. It becomes something like that. ``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 sometimes generates noise and adversely affects logic circuits and the like. Also, as shown in Figure B compared to Figure A,
The output voltage V of the power supply circuit of the thermal head also fluctuates greatly, and a problem arises in that desired energy cannot be supplied to each unit heating element unless a new power supply voltage compensation circuit is provided. 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 the applied pulses are generated when the thermal head driving method of the present invention is used, and corresponds to FIG. 6. In the figure, times T ₁ , T ₂ . . . approximately correspond to the center positions of the respective applied pulses 23. As a result, the total current I required by the thermal head changes as shown in FIG. 2A with respect to the elapsed time t, and the output voltage V of the power supply circuit changes as shown in FIG. The fluctuations are more gradual compared to . In other words, 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 with reference to Examples below. 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 for the dot of interest, and the applied pulse calculation circuit 33 calculates the heat storage state of the unit heating element corresponding to the dot of interest based on this. The applied pulse arithmetic circuit 33 is a circuit in which the first and second arithmetic units 14 and 17 shown in FIG. Output to. The pulse waveform ROM 34 contains applied pulse width information 19
As address information, the generation timing and time width of the applied pulse are read out in the form of decomposed unit pulse information 35 in 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 this cycle is set to 0.1mS in this example, 1mS
The applied pulse consists of 10 unit pulses,
The applied pulse of 0.8 mS consists of 8 unit pulses. Now, assuming that the time width of the applied pulse applied to each unit heating element is set in 8 steps between 0.5 and 1.2 mS, the relationship between the applied pulse width information 19 and the unit pulse information 35 is as follows. It will look like Table 1. However, in this table, information "1" represents a state in which a unit pulse exists, and information "0" represents a state in which there is no unit pulse.

[Table] The unit pulse information 35 is supplied to the transfer signal buffer 36 as information of 8 bits each, and is written in 1 bit each divided into 8 address areas A1 to A8 under the control of the address control circuit 37. . Each of the address areas A1 to A8 has a bit capacity equivalent to the total number of pixels in one line, and when the unit pulse information 35 is output for all pixels in one line, the transfer signal buffer 36 has a bit capacity corresponding to the total number of pixels in one line. This means that writing of all pulse information for minutes 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), the image signal 39 of the dot of interest is a non-printed dot (white dot).
When corresponding to , all "0" information is written in the corresponding position of each address area A1 to A8, regardless of the contents of the unit pulse information 35. 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 as cycle image data 41. It is supplied to the thermal head 42. This cycle image data 41 is set in a shift register (not shown) mounted on the thermal head 42, and is further latched in a latch circuit (not shown), after which energization control of each unit heating element is performed. At this time, in the part of the unit heating element corresponding to the information "1" constituting the cycle image data 41,
A current of 0.1 mS is applied, and no current is applied to the part of the unit heating 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, this second
A second energization control is performed based on the information in the 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 to drive the step motor 46 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 rear 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, costs required for noise countermeasures, power supply stabilization measures, etc. can be reduced, and recorded or displayed images with more uniform image quality can be obtained. Furthermore, in the present invention, the generation timing of each applied pulse may be controlled so that the center positions of the applied pulses having a time width corresponding to the applied energy coincide with each other. Therefore, control is simple, and moreover, the power consumption of each heating element of the thermal head increases and decreases symmetrically with the peak at a predetermined point, and these starting points vary depending on the pulse width applied to each heating element. There will be large variations. As a result, the starting point of power consumption of each unit heating element during recording with the thermal head is relatively widely dispersed. This will be compared with a method in which the end points of the head drive time until the temperature of each unit heating element reaches the minimum temperature necessary for coloring the thermal paper are made to coincide.
In this method, electricity is applied until the minimum temperature required for color development is reached, so the time required is relatively short. Therefore, the starting point of power consumption of each heating element hardly varies depending on the amount of heat storage of the unit heating element.
Therefore, with this method, the inrush current may increase significantly compared to the present invention. In this way, the present invention reduces inrush current, so
This has the advantage that noise is much less likely to be generated, and noise countermeasures are also easier.

[Brief explanation of the drawing]

FIG. 1 is a waveform diagram showing an example of applied pulses applied to each unit heating element when using the thermal head driving method of the present invention, and FIG. 2A is a time diagram of the total current consumption of the thermal head according to the present invention. Figure 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 a recording device to which the present invention is applied. Figure 4 is a block diagram of a thermal head using a conventional thermal head driving method, Figure 5 is an explanatory diagram showing the relationship between a dot of interest and a reference dot, and Figure 6 is an illustration of the voltage applied to each unit heating element using a conventional thermal head driving method. FIG. 7A is a waveform diagram showing an example of the applied pulses, and FIG. 7A is a diagram showing an example of the temporal required value of the total current consumption of the conventional thermal head.
FIG. 5B is a characteristic diagram showing an example of a change in the output voltage of the power supply in this case. 34... Pulse waveform ROM, 37... Transfer signal buffer, 41... Cycle image data, 42...
thermal head.

Claims (1)

[Scope of Claims] 1. Application pulses having a time width corresponding to the applied energy to a plurality of heating elements constituting the thermal head are supplied, and the thermal energy generated by these heating elements is used to thermally record or display. The method is characterized in that the generation timing of the applied pulses applied to each heating element is controlled so that the generation times of approximately the center positions of all the applied pulses that occur temporally overlappingly coincide with each other. Thermal head drive method.