JPS6158763A - Thermal head driving device - Google Patents

Abstract

PURPOSE:To enable high quality printing by reading from ROM the value of the optimum width or the most suitable wave height of the pulse applied to a thermal head, and controlling it, based on the information of the means resis tance value of each register of the head and the temperature of the supporting base plate of the head. CONSTITUTION:A thermal head driving device is composed of following means: the indicating means 11 for indicating the mean resistance value of each exothermic resistance element in the thermal head of a line printer as an electric signal; the temperature measuring means 12 for measuring the temperature of the supporting base plate of the thermal head, the read only memory (ROM)13 in which the optimum value of applied energy to the head is written in relation to the mean resistance value of the kead and the temperature of the supporting base plate; and the controlling means 14 in which while reading from ROM13 the value of the pulse width or the wave height corresponding to the optimum energy applied to the head, using, as an address information, the means resistance value indicated in the mean resistance indicating means 11 and the measured temperature by the temperature measuring means 12, whereby the applied energy is regulated accordingly thereto.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a thermal head driving device for performing a printing operation while controlling the energy applied to a line-type thermal head.

"Prior Art" Thermal heads are widely used in recording devices such as thermosensitive color recording devices and thermal transfer recording devices, and in display devices that display images using magnetized latent images. This thermal head has a problem in that the average resistance value varies considerably from product to product due to manufacturing errors when forming the heating resistor on the substrate. For example, in a thick-film thermal head in which a heating resistor is formed by printing technology, the average resistance value varies by about ±10%. Further, in a thin film type thermal head in which a heating resistor is formed by vapor deposition technology, a variation of about ±3% occurs in the average resistance value. In this way, the average resistance value of thermal heads varies depending on the product even under the same conditions, but this resistance value also changes due to temperature fluctuations. Therefore, if a pulse with the same voltage and duration is applied to all thermal heads, there will be variations in print density depending on the product and the temperature of the support substrate on which the heating resistor is attached. Become.

Therefore, the energy applied to the thermal head has been controlled in accordance with the average resistance value of the thermal head and the temperature of the support substrate.

FIG. 5 is for explaining this situation.

In the figure, a curve 11I represents the voltage applied to the thermal head having the highest average resistance value in relation to the temperature of the support substrate. For example, at the lowest temperature TL, the temperature difference from the optimum temperature for printing is the largest and the current does not flow, so the highest applied voltage must be set.On the other hand, at the highest temperature To , If the voltage ■1 is set, which is quite low,
This results in optimal printing.

On the other hand, curves! L represents the relationship between the applied voltage and substrate temperature in the thermal head that has the lowest average resistance value, and optimal printing can be achieved by appropriately varying the applied voltage between voltages VLH and VLL. It will be possible to do it.

Curve βA represents the characteristics of a thermal head having an average resistance value.

For the above reasons, in conventional thermal head driving devices, the average resistance value of the thermal head installed in a recording device, etc. is measured at a specific temperature (for example, temperature T, ), and as shown in Fig. A reference value of applied voltage with respect to temperature was set. The temperature state of the support substrate of the thermal head is detected using a temperature detection element such as a thermistor, and the applied energy is controlled by increasing or decreasing the applied voltage as appropriate.

However, in such a thermal head drive device, (i
) When assembling a recording device, etc., it was necessary to adjust the output voltage of the power supply circuit for each thermal head and set the applied voltage to a desired value. Such work was similarly necessary when replacing the thermal head. (ii
) In addition, conventional devices also controlled the applied voltage according to changes in the substrate temperature, but this was a relatively rough correction using a correction circuit, and depending on the individual average resistance value or the temperature of the substrate, inappropriate energy could be generated. was applied to the thermal head. That is, when the thermal head is replaced or a printing operation is performed at a predetermined substrate temperature, an unsatisfactory printing result may be obtained in some cases.

"Problems to be Solved by the Invention" In view of the above circumstances, the present invention provides a method for properly correcting the applied energy without correcting the power supply voltage even if the average resistance value or the temperature of the supporting substrate differs. The purpose of the present invention is to provide a thermal head driving device that can perform the following functions.

"Means for Solving the Problems" In the present invention, as shown in principle in FIG. The display means 11, the temperature measurement means 12 such as a thermistor used to measure the temperature of the support substrate of the thermal head, and the appropriate amount of applied energy corresponding to the relationship between the average resistance value of the thermal head and the temperature of the support substrate. The average resistance value displayed by the average resistance value display means 11 and the temperature measured by the temperature measurement means 12 are both supplied to the read-only memory 13 as address information. The thermal head driving device is equipped with read-only memory reading control means 14 for reading out the time width or peak value of the applied pulse corresponding to the appropriate amount of applied energy to the thermal head.

In this thermal head drive device, the optimum amount of applied energy (applied pulse width or applied pulse peak value) is stored in read-only memory as a table based on the relationship between average resistance value and temperature. Printing operation can be performed using the pulse width or peak value of energy.

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

FIG. 2 shows the main parts of a recording section using the thermal head driving device of this embodiment. The thermal head 21 used as a print head in this recording section is a line type print head, and a group of unit heating elements 22 arranged in a - row are selectively energized and heated to scan a thermal recording paper (not shown) using a rusk scanning method. Record with . Unit heating element group 2
2 are divided into four groups and driven, thereby reducing the size of the power supply (not shown).

This thermal head 21 measures the resistance value of each unit heating element in advance under a specific temperature, and an average value is calculated from this.

To measure the resistance value, it is sufficient to selectively energize the unit heating elements one by one and measure the current corresponding to each applied voltage. Thermal head 2 obtained in this way
The average resistance value of 1 is displayed as average resistance value information 24 by the dip switch 23. dip switch 2
3 may be replaced by resistance trimming.

Incidentally, a unit heating element group 22 is formed on the support substrate of the thermal head 22, and a temperature detection element 25 for measuring the substrate temperature is attached to the center of this substrate. As the temperature detection element 25, for example, a thermistor or a positor is used.

A detection signal 26 from the temperature detection element 25 is input to an A/D converter 27, where it is analog-to-digital converted to create temperature information 28. Average resistance value information 24 and temperature information 28 are supplied to pulse width table ROM 29 as address information.

The pulse width table ROM 29 is a read-only memory for determining the energy for printing on the thermal head 21 based on the pulse width. The ROM 29 reads out desired pulse width information 31 by using a predetermined number of bits of average resistance value information 24 as an X address, and using another predetermined number of bits of temperature information 28 as a Y address. In the figure, five types of pulse widths W1 to W are pulse width table ROM, 2
9, but it is of course possible to set even more pulse widths. These pulse widths WI -W5 are values determined by experiments or calculations as optimal values for the average resistance value and substrate temperature, and are common to each recording section. Pulse width information 31 is timing control ROM
32 as part of the address information.

Now, the timing control ROM 32 is supplied with count value information 34 representing a count value from a counter 33 that counts clocks (not shown), and uses this count value information 34 and pulse width information 31 as address information to set various timings. Generate a signal. Typical of these are the applied pulse signal 36, the motor transport start signal 37, and the count-up signal 38. Among these, the applied pulse signal 36 is a signal representing the generation timing of the applied pulse and its pulse width. When driving one line by dividing it into four times, four applied pulse signals 36.
~364 occurs (Fig. 3 a1 to a4). The motor conveyance start signal 37 (FIG. 3b) is a timing signal for sub-scanning the recording paper to the next recording position after one line of recording has been performed. Count up signal 38 (3rd
The signal shown in FIG. C) is generated as the last signal in a series of timing signals for one line, which clears the counter 33 and starts reading control for the next line.

FIG. 4 shows the memory structure within this timing control ROM. Timing control ROM32 is 0~A-
Address 1 is a memory area related to pulse width W1. If the first address 0 of this memory area is specified by the pulse width information 31, the applied pulse signal 36. 364, a motor transport start signal 37, a count up signal 38, etc., are output. Here, apply pulse signal 3
61-36. The pulse width of each will be set to Wl.

Overall control of the timing control ROM 32 is performed by a rask processing start signal 42 output from a sequence controller 41 shown in FIG. The sequence controller 41 reads out the video signal from the video buffer 44 into which the video signal 43 has been written in synchronization with the rask processing start signal 42, and applies the applied pulse signal 36. ~
The thermal head 21 is driven four times at an angle of 36 degrees. Thereafter, the recording paper (not shown) is sub-scanned by one line by a conveyance mechanism (also not shown). In this way, recording is performed line by line.

When the unit heating element group 22 repeatedly generates heat by driving the thermal head 21 and the temperature of the support substrate rises, the A/D
Temperature information 28 output from converter 27 changes. Assuming that pulse width information 31 indicating the pulse width W2 is thereby output, address A of the timing control ROM 32 is specified by this pulse width information. The address A=B-1 of the timing control ROM 32 is the pulse width W.
This is a memory area related to 2. Therefore, the print pulse signal 3 output when the count value information 34 counts up
6. .about.364 are signals each having a pulse width W2. The motor conveyance start signal 37 and the count-up signal 38 are output after being delayed by a predetermined time in accordance with the increase in pulse width.

Address B-C-1 of the timing control ROM 32 is a memory area with a pulse width W3, and similarly, address B-C-1 is a memory area with a pulse width W3.
Area 18 is a memory area with a pulse width W. Therefore, the thermal head 21 is appropriately driven with the pulse width determined each time based on the average resistance value information 24 and the temperature information 28. When the thermal head 21 is replaced, new average resistance value information 24 is displayed by the DIP switch 23 etc. attached to the new thermal head, so a good recording surface can be obtained immediately without any power adjustment. .

"Effects of the Invention" As explained above, according to the present invention, the table for determining the amount of applied energy is written in the read-only memory, so even if the temperature of the supporting substrate changes over a wide range, all of these Therefore, it is possible to always determine the appropriate energy to be applied.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the basic configuration of the present invention, FIG. 2 is a block diagram showing the main parts of a recording section using a thermal head drive device in an embodiment of the present invention, and FIG. 3 is a block diagram of this embodiment. 4 is a diagram showing the memory configuration of this timing control ROM, and FIG. 5 is an explanatory diagram for explaining conventional applied energy control. 11... Average resistance value display means, 12...
・Temperature measurement means, 13... Read-only memory, 14...
...Read-only memory reading control means, 21...
... Thermal head, 23 ... DIP switch, 25 ... Temperature detection element, 29 ... Pulse width table ROM. 31...Pulse width'tf information, 41...
・Sequence controller. Applicant: Fuji Xerox Co., Ltd. Representative
Patent Attorney Ume Yu Yamauchi 1st
Figure ] 2 Figure 4 Figure 2 Figure 3 Figure ■L1oIH Ontaka

Claims (1)

[Claims] An average resistance value display means for expressing the average resistance value of a line-type thermal head as an electrical signal, a temperature measurement means for measuring the temperature of a support substrate of the thermal head, and an average resistance value of the thermal head and a temperature of the support substrate. Read only the read-only memory in which a value corresponding to the appropriate amount of applied energy is written, and read both the average resistance value displayed by the average resistance value display means and the temperature measured by the temperature measurement means as address information.・Only・
A thermal head driving device comprising read-only memory reading control means for reading out the time width or peak value of an applied pulse that is supplied to a memory and corresponds to an appropriate amount of applied energy to the thermal head.