JPS62121072A - Controller for thermal head - Google Patents

Abstract

PURPOSE:To enable recording with little nonuniformity in density to be performed inexpensively, by recording while switching between an unchanged applied pulse width and a changed applied pulse width for a predetermined period of time after the applied pulse width is changed. CONSTITUTION:A central processor (CPU) 3 causes a temperature signal S3 relating to a thermal head 9 sent from a thermistor 27 to be once stored in a RAM 15, calculates a temperature variation based on the temperature value stored in the RAM 15, and again stores the calculated value into the RAM 15. The CPU 3 reads the temperature variation from the RAM 15, compares it with a threshold preset in a ROM 13, and sends a command for changing the width of an applied pulse to an applied pulse width controlling circuit 11 when the temperature variation is larger than a threshold. For a predetermined period of time after the change in the applied pulse width, a command for switching between the pulse width before the change and the pulse width after the change is given to the applied pulse width controlling circuit 11.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a thermal head control device that is inexpensive and capable of recording with less unevenness by m degrees.

[Technical background of the invention]

Conventionally, when recording with a thermal head, the temperature of the thermal head is detected by a thermistor attached to the heat sink of the thermal head, and a data table indicating the pulse width with respect to temperature is detected and the thermal signal is detected every time the temperature of the thermal head changes. Varying the width of the applied pulse to the head is performed.

The reason for performing recording in this manner is to obtain printing with uniform density even if the temperature of the thermal head changes.

[Problems with background technology]

In the thermal head control method described above, the pulse width value is affected by the resolution of the analog-to-digital converter that converts the humidity signal from the thermistor into analog and digital, and the pulse width resolution, and the pulse width value can be changed finely. In order to achieve this, it is necessary to increase the resolution of the analog-to-digital converter or to increase the resolution during the pulse.

However, to increase the resolution of the analog-to-digital converter, an expensive analog-to-digital converter is required, and to increase the resolution during pulses, the number of integrated circuits used increases, resulting in an increase in cost. For this reason, conventional thermal head control devices perform rough control without making small changes in the pulse width, and as a result, the few lines immediately before changing the pulse width have a pulse width that is too large compared to the temperature of the thermal head. The density becomes high, and conversely, in the few lines immediately after the pulse width is changed, the density becomes thin because the pulse width is too small, which has the disadvantage that density unevenness occurs before and after the pulse width change.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a thermal head control device that is inexpensive and capable of recording with less density unevenness in order to solve the above-mentioned problems.

[Summary of the invention]

In order to achieve the above object, the present invention provides a thermal head, an applied pulse width control circuit for applying an applied pulse among predetermined pulses to the thermal head, a temperature measuring means for measuring the temperature of the thermal head, and a temperature measuring means for measuring the temperature of the thermal head. The temperature change value is extracted from the temperature information of the thermal head, and when this temperature change value exceeds a certain value, the applied pulse width is changed once, and then the applied pulse width is switched between two applied pulses, one before the change and one after the change, for a predetermined period of time. and a control section that gives an instruction to the control circuit during the application pulse.

[Embodiments of the invention]

Examples of the present invention will be described in detail below.

FIG. 1 is a block diagram showing the configuration of a thermal recording apparatus equipped with a thermal head control device according to this embodiment. In the figure, the reference clock generation circuit 1 has a reference clock signal C
L is generated and supplied to the central processing unit (CPU) 3 and control clock generation circuit 5. The control clock generation circuit 5 generates an image signal synchronization signal S1 from the reference clock signal CL, and transmits this to the image reading section 7. It is supplied to the thermal head 9. The image reading unit 7 reads the image and reads the read image M.
S2 enters the thermal head 9. The thermal head 9 is synchronized with the synchronization signal S1, inputs the image signal S2, and performs recording on a recording paper (not shown) according to the applied pulse signal S5 sent from the control circuit 11 during the applied pulse. CPU3. Read-only memory (ROM)13. A control section 17 is formed by a random access memory (RAM) 15 . A parallel input/output port (PIO) 19 is an interface between the control unit 17 and other elements.

PIO19, CPU3. ROM13. The RAM 15 and the applied pulse width control circuit 11 are interconnected by an 88itBus 21. The motor control circuit 23 is PI01
Motor control signal S6 sent from CPtJ3 via 9
As a result, a motor drive signal S7 is created and supplied to the motor 25. The motor 25 is a motor for feeding recording paper. The thermistor 27 measures the temperature of the thermal head 9, and a signal S3 representing the temperature of the thermal head 9 is converted into a digital value by an analog-to-digital converter (A/D converter) 29 and input to the CPU 3 via the PIO 19. The application pulse control circuit 11 supplies an application pulse signal S5 having a predetermined width to the thermal head 9 in accordance with a command from the CPU 3. In the control section 17, the CPU 3 performs predetermined arithmetic processing based on the program stored in the ROM 13. Note that reference numeral 31 is a power source for the thermal head 9.

Next, the operation of this embodiment will be explained.

The image 4 & reading section 7 starts outputting the image signal S2 in response to a reading start signal S4 sent from the CPU 3 via the PIO 19. The synchronization signal S1 of the image signal is generated by the control clock generation circuit 5, and is generated by the image reading section 7 and the thermal head 9.
is input. The motor control circuit 23 receives the motor control signal S6 sent from CPLJ3 via PI019.
A motor drive signal S7 for moving the motor 25 is created.

The rotation of this motor 25 feeds the recording paper.

A signal S3 indicating the temperature from the thermistor 27 located on the thermal head 9 passes through the A/D converter 29, is converted into a digital value, and is input to the CPtJ3 via the PIO 19. The control unit 17 performs control to change the pulse every time this digital value changes by a certain value. That is C
The PU 3 temporarily stores the temperature signal S3 of the thermal head 9 sent from the thermistor 27 in the RAM 15, calculates a temperature change value based on the temperature value stored in the RAM 15, and stores it in the RAM 15 again. Then, this temperature change value is read out from the RAM 15 and compared with a threshold value preset in the ROM 13, and when the temperature change value is larger than the threshold value, the applied pulse width control circuit 11 is commanded to change the applied pulse width, and the applied pulse width is increased. During a predetermined period after the pulse width changes, an instruction is given to the applied pulse width control circuit 1 to switch between the two applied pulses before and after the change.

FIG. 2 is a flowchart showing the operation of this control section 17. As mentioned above, when the temperature change value is larger than the threshold value, the CPU 3 determines that it is a changing point in the pulse (step 201), and instructs the applied pulse width control circuit 11 to change the applied pulse width to control the applied pulse width. The circuit 11 applies an applied pulse signal S5 having a different pulse length than before.
is supplied to the thermal head 9 (step 202). Next, when recording of one line is completed (step 203),
The CPU 3 instructs the applied pulse width control circuit 11 to return the middle of the applied pulse to its original state, and the applied pulse width control circuit 11 returns the middle of the pulse to its original state (step 204). Next, when the recording of one line is completed (step 205), the above operation is repeated until the α-th line is reached, and when the α-th line is reached (step 206), the CPU 3 again changes the applied pulse width tI.
A command is given to the I11111 circuit 11 to change the duration of the applied pulse (step 207). Furthermore, step 206
The value of α is set in advance to a value of 2 or more.

Therefore, for example, when the value of α is set to 3, in this embodiment, the pulse of the applied pulse is switched between before and after the change for each line during the three lines after the change point. Since recording is performed, there is no sudden change in the pulse before and after the change point, and m degree non-uniformity can be reduced.

In this example, after first changing the applied pulse,
Control is performed such as switching between the pulse before and after the change while recording a certain line, but it is also possible to switch between the pulses during a certain period of time after first changing the applied pulse, or change the pulse during the applied pulse. Pulse 1] may be switched while the value of the thermal head is within a constant value after the initial change.

[Efficacy of invention Song Dynasty]

As explained in detail above, according to the present invention, recording is performed by switching between the two applied pulses before and after the change for a predetermined period after changing the applied pulse, resulting in low cost and less density unevenness. Ill ml of thermal head that can record
equipment can be provided.

[Brief explanation of drawings]

FIG. 1 shows the control of a thermal head according to an embodiment of the present invention.
FIG. 2 is a block diagram of the configuration of a recording apparatus having an ilI device, and is a flowchart showing the operation of the control section. 9... Thermal head, 11... Applied pulse width control circuit, 17... Control unit, 27... Thermistor. Figure 1 Figure 2

Claims (1)

[Scope of Claims] A thermal head; An applied pulse width control circuit for applying an applied pulse of a predetermined pulse width to the thermal head; Temperature measuring means for measuring the temperature of the thermal head; and Measured temperature of the thermal head. A temperature change value is calculated from the information, and when this temperature change value exceeds a certain value, the applied pulse width is changed once, and then an instruction to switch between the two applied pulse widths before and after the change is applied for a predetermined period of time. 1. A control device for a thermal head, comprising: a control section for controlling a pulse width control circuit.