JPH04122653A - Thermal recorder - Google Patents

Abstract

PURPOSE:To avoid differences in printing density among blocks by providing a power source capable of controlling output voltage with control signals and setting applying voltage based on combined resistance value of divided each block of a thermal head. CONSTITUTION:Supply voltage is made to be variable dependent on combined resistance values among blocks and heat energy to be generated at a heat generating resistor is made to be constant. When a combined resistance value r1 in 1 block is different from combined resistance values r2, r3, r4 in other 3 blocks, assuming that a supply voltage at the time that voltage is applied to the r1 is V1 and a supply voltage at the time that voltage is applied to either l block out of r2-r4 is V2, the ratio of the V1 and V2 is made to be as the expression (I), where r0 represents an internal impedance of the power source. Thus, the supply voltage is controlled with such a ratio, so that heat energies to be generated among blocks become equal, so that no differences occur in printing density.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a thermal recording device using a line-scanning thermal head, which is mounted on a facsimile machine, a printer device, a plotter device, etc.

(Prior Art) Fig. 2 shows the configuration of a facsimile machine as an example of a device using this type of thermal head, in which 1 is a thermal head, 2 is a platen roller, and 3 is a rolled-up facsimile machine. This is thermal recording paper, and the recording section is made up of these sheets. The transmission document reading section includes a pickup roller 4 that feeds the document, a pair of separating/feeding rollers 5 that separates and supplies the multiple sheets of document sent one by one, and a pair of transport rollers that conveys the supplied document. 6 and 7, a light source 8 that illuminates the document being conveyed, mirrors 9 and 9 that change the optical path of light reflected from the surface of the document, and a sensor 11 that photoelectrically converts the image of the lens IO1 for image formation. 12 is an FCU (facsimile control unit) that controls the operation of the facsimile, and 13 is a PSU (power supply).

FIG. 3 shows the flow of recording data in a facsimile. After the received image data is processed by the modem 14, it passes through the FCU 12, becomes recorded image data, and is sent to the thermal radar 1. As another flow,
The read image data read by the scanner (original reading unit) 15 becomes recorded image data after passing through the FCU 12.
Thermal is sent to Rad 1. On the other hand, power is sent from the PSU 13 to the thermal head 1 to cause the heating resistor to generate heat, thereby recording image information on the thermal recording paper.

Incidentally, the thermal head 1 has a large number of heating resistors arranged in the width direction of the recording paper. The heating resistor is usually divided into four or two parts and driven. FIG. 4 schematically shows the internal configuration of the thermal head. For example, an A4 size thermal head has 1728 dots when converted to 8 dots/M, and if it is divided into four, the number of heating resistors per block is 1728/M.
4 = 432 dots, but this is not actually the case.

This is because the driver IC can only divide every 64 dots, that is, 1728/64 = 27 is divided into 4, so 448 dots x 3 and 384 dots x 1 are divided into 4.
It will be split.

Therefore, if the average resistance value of the heating resistor is r, the combined resistance value of each block is r/448 or r/384,
Differences occur between blocks. However, even when the combined resistance values differ in this way, the power supply voltage is constant, so the current values flowing between the blocks will differ.

(Problems to be Solved by the Invention) As described above, in a thermal recording device using a conventional split drive type line scanning thermal head, the combined resistance between each block is different, and therefore the current value flowing between the blocks is different. As a result, there was a problem that a difference occurred in print density. The reason for this is that blocks with a low combined resistance value have a large amount of current flowing through them, so the voltage supplied to the thermal head decreases due to the internal impedance of the power supply, and as a result, the energy generated by the thermal head decreases. is possible.

The present invention aims to solve the problems of the prior art, and it is an object of the present invention to provide a thermal recording device that eliminates the difference in print density between blocks.

(Means for Solving the Problem) In order to achieve this object, the present invention includes a power supply whose output voltage can be controlled by a control signal, and applies voltage based on the combined resistance value of each divided block of the thermal head. This is to set the voltage.

(Function) According to this configuration, the difference in applied voltage due to the difference in the number of dots between blocks is corrected, so it is possible to obtain a uniform recorded image density.

(Example) Embodiments will be described in detail below with reference to the drawings.

FIG. 1 shows one embodiment of the present invention, and is an equivalent representation of a circuit between a power source and a thermal head.

■ is the power supply voltage, r□ is the internal impedance of the power supply, r1
~r4 is the combined resistance value of the heating resistors of each block divided into four, and 81~s4 are on/off switches for the strobe signal of each block.

In the conventional configuration, the power supply voltages V were always the same even if the combined resistance values between the blocks were different.

In this embodiment, the power supply voltage is made variable according to the combined resistance value between the blocks, and the thermal energy generated by the heating resistor is kept constant. Now, the combined resistance value rl of one block is the combined resistance value r2+ r3+ of the other three blocks.
If r4 is different, let vl be the power supply voltage when voltage is applied to rl, and V2 be the power supply voltage when voltage is applied to any one block of r2 to r4, then the ratio of vl and V2 is as follows: Make it.

By controlling the power supply voltage at the ratio described above, the thermal energy generated between each block becomes equal, and as a result, there is no difference in print density.

(Effects of the Invention) As explained above, according to the present invention, since the power supply voltage to be applied is set according to the combined resistance value of the heating resistors of each divided block of the thermal head, The thermal energy generated becomes equal, and printing can be done with uniform density.

[Brief explanation of drawings]

FIG. 1 is a diagram equivalently representing a circuit between a power supply and a thermal head according to an embodiment of the present invention, and FIG. 2 is a schematic configuration diagram of a facsimile machine as an example of a device using a line scanning type thermal head. , FIG. 3 is a block diagram showing the flow of image data in the facsimile machine, and FIG. 4 is a diagram showing the division of the line scanning type thermal head into blocks. ■...Thermal head, 12...FCU, 13
...PSU, 14...Modem, 15...Scanner

Claims (1)

[Claims] A thermal recording device that uses a line scanning type thermal head and drives the thermal head in divisions, which is equipped with a power source whose output voltage can be controlled by a control signal, and has a combined resistance of heating resistors of each divided block of the thermal head. A thermal recording device characterized in that an applied voltage is set based on a value.