JPH0319854A - Control of thermal head - Google Patents

Abstract

PURPOSE:To achieve equalization of density of an image or printing by a method wherein the title thermal head is so controlled as to lengthen electrification time of a thermal head during a required time width from a point of time when feed of a printing signal is started. CONSTITUTION:Thermal heads 9a to 9c are arranged at equal intervals L on recording paper 6, and the recording paper 6 is principally scanned in the arrow B direction whenever the thermal heads 9a to 9c record an image by subsidiarily scanning in the arrow A direction. For a time width corresponding to a specific interval L1 from a position P1 wherein each thermal head 9a to 9c starts subsidiary scanning, electrification time of each thermal head 9a to 9c is increased and after scanning L1, are electrification time is controlled to a stationary state. A heating quantity of each thermal head 9a to 9c is increased during L1 and after ending recording during L1, recording is performed by heating and heat accumulation due to stationary electrification. Therefore, difference in density can be reduced.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a thermal head control method suitable for use in an image recording device configured to record characters, figures, images, etc. using a thermal head. More specifically, the present invention relates to a thermal head control method for reducing density unevenness due to the heat storage effect of the thermal head.

[Conventional technology]

2. Description of the Related Art Some image recording apparatuses such as printing printers and image printers use a thermal head as a recording means.

The thermal head has a structure in which a large number of heating resistive elements (hereinafter referred to as heating elements) are bonded to a flat ceramic or aluminum substrate.

When recording an image, the thermal head 32 is scanned over the thermal paper 3l as shown by arrow A in FIG. , record letters, figures, etc. on the heat-sensitive paper 3l.

[Problem to be solved by the invention]

The thermal head 32 generates heat approximately in proportion to the energization time, but since the amount of heat generated is not saturated at the initial stage of driving, a sufficient amount of heat is not obtained, resulting in poor color development during printing.

Therefore, the density of the image recorded on the thermal paper 3l changes from low density to high density as shown in FIG. does not have a uniform concentration.

On the other hand, the density change can be reduced by increasing the amount of current supplied to the heating element during one line printing and generating heat in the saturated region. However, in this case, power consumption will be large,
This not only shortens the life of the thermal head, but also causes problems such as a decrease in recording speed.

In particular, in a printer in which, for example, three thermal heads 32 are arranged at equal intervals as shown by the imaginary lines in FIG. At the connecting positions of the images recorded by each thermal head 32, a density difference becomes noticeable as shown in FIG. 7(B), and a high-quality image cannot be obtained.

The present invention has been made to solve the above problems, and its purpose is to provide a method for controlling a thermal head that can reduce density unevenness during image recording.

[Means and Effects for Solving the Problems] The object of the present invention is to provide a thermal head control method for supplying a print signal to a thermal head that scans on thermal paper to perform print recording on the thermal paper. This is achieved by a thermal head control method that controls the energization time of the thermal head to be extended by a desired time width from the start of supply.

That is, the supply time of the print signal is controlled to be long for a desired time from the start of the print signal supply, and after the elapse of the desired time, the time width of the print signal is controlled to a steady state. As a result, before heat is stored in the thermal head, the recording density is increased by a print signal with a large amount of heat generated, and after the desired time has elapsed, image recording is performed using the heat stored and the heat generated from the thermal head, so the recording density increases. It is possible to equalize the

[Embodiment]

Embodiments of the present invention will be described below based on the accompanying drawings. In addition, in explaining this embodiment, FIGS.
Explain how to control the thermal head with reference to the diagram,
Next, an enlarged copying machine suitable for implementing the present control method will be described with reference to FIG. 4 and subsequent figures.

As shown in FIG. 1(A), on the record 6 there are
Three thermal heads 9a, 9b, and 9c are arranged for each. And the record 6 is the thermal head 9a-9
Each time C performs one scan (sub-scan) in the direction of arrow A to record an image, it is conveyed a predetermined distance (main scan) in the direction of arrow B.

In this embodiment, each thermal head 9a to 9b is set at a predetermined interval L1, e.g.
In the time width corresponding to about 0 mm, the energizing time of each thermal head 98 to 9C is controlled to be increased as shown in FIG. Control. The control of the energization time, in other words, the control of the energization amount, will be explained later with reference to FIG. 2.

To energize each of the thermal heads 9a to 9C as described above,
This is performed based on a print signal, which will be described later. Therefore, the energization control greatly controls the energization time of each thermal head 9a to 9C at the start of supply of print signals, and is controlled to be energized in a steady state from the time when recording of the predetermined interval L1 is completed.

By performing such energization control, the amount of heat generated by each thermal head 9a to 9c becomes large between Ll, and
After the recording is completed, recording begins due to heat generation and heat storage due to steady electricity supply. As a result, the density of the recorded image is
As shown in FIG. 1(C), the density is equalized, and in particular, the difference in density at the print boundary position Pl between the two thermal heads can be reduced. According to conventional control, Fig. 1 (C
), a density difference as shown by the virtual line appeared, but by controlling the energization of each thermal head 9a to 9c as described above, the density difference can be reduced.

Note that the setting of the interval L1 is for each thermal head 9a to
It can be changed arbitrarily depending on the number of heat generating elements 9c, the properties of the recording board 6, etc., and is not limited to about 10 ribs.

Further, as long as the life of the thermal heads 9a to 9c is not affected, it is also possible to make the concentration uniform by keeping the amount of change in the energization time constant, as shown by the dotted line in FIG.

Next, control of the energization time will be explained with reference to FIG.

The heating elements of each thermal head 9a to 9C are supplied with a pulse signal v1 as shown in FIG. 2 in response to the print signal, and the energization time is controlled by the rise time width t of the pulse signal v1. It will be done. Assume now that the period width T of the pulse signal V1 is 1.8 ms, and the rising time width t is, for example, 1.5 m while scanning the interval L1.
If the temperature is controlled to s, the amount of heat generated will increase corresponding to the time width t. Also, with the end of recording the interval L1, the time width t
If the time is controlled to be as short as about 0.9 μs, the amount of heat generated will be reduced, and the concentration will be equalized as described above.

Note that the above-described energization control of each thermal head can also be performed in relation to the amount of heat storage of each thermal head.

FIG. 3 shows a cross-sectional structure of each of the thermal heads 9a to 9C, in which a large number of heating elements 33 are attached, for example, to a ceramic base Fi34 by adhesive or the like. A temperature detection element 35 such as a thermistor is provided on a part of the ceramic substrate 34, and the rise time t of the pulse signal (2) is controlled by the temperature detection signal (2).

According to the thermal head control method described above, the heat generation of the thermal head can be controlled in accordance with the amount of heat storage, so that it is possible to equalize the recording density as shown in FIG. 1(B).

Next, an application example of the present invention will be explained with reference to FIGS. 4 to 6.

In addition, the energization time after returning to the steady state is at a constant level, but by uniformly increasing or decreasing the energization time level in the steady state over the entire area, the amount of heat generated in the steady state can be adjusted. The coloring density of the thermosensitive color 6 can be adjusted.

FIG. 4 is a perspective view of an enlarged copying machine that implements the thermal head control method according to the present invention. This enlarged copying machine is a device that enlarges and copies, for example, an A4 size original into A1 size, and is composed of an original reading device 1 and a recording device W2.

The reading device 1 is equipped with an image sensor that scans the document in the width direction and reads the image. When the document 4 is supplied to the reading device 1 from the document insertion port 3, the document 4 is conveyed so as to be scanned by the image sensor. The document is discharged from the document discharge port 5.

The recording device 2 stores a roll of thermal paper 6 (corresponding to the recording paper) with a width of 594 cm, and has three thermal heads that print and scan the thermal paper 6 in the width direction (sub-scanning direction). It is equipped with The three thermal heads have 64 dots within the effective main scanning width and are arranged at equal intervals on the same scanning line.
Each thermal head scans the thermal paper 6 at the same distance over the same distance, thereby printing one line across the width. The thermal paper 6 on which predetermined recording has been performed is then discharged from the discharge port 12.

FIG. 5 is a schematic diagram of the recording device 2. As shown in FIG. The heat-sensitive sleeve 6 wound into a roll is conveyed by a conveyance roller 7 made of chloroprene rubber, polyacetal, or the like. The thermal head 9 is fixed to the base lO, and the platen 1
Printing is performed by scanning the heat-sensitive coat 6 in contact with the heat-sensitive coat 6 supported by the heat-sensitive coat 1 . When one printing scan over the entire width of the heat-sensitive paper 6 is completed, the head 9 starts returning to the scanning start position, and at the same time, a motor (not shown) that rotationally drives the conveyance roller 7 is activated to print the heat-sensitive paper 6. The conveying roller 7 is rotationally driven so as to convey the main scanning distance of the head 9 in the direction not shown by arrow D. After the thermal paper 6 is conveyed by the main scanning distance of the head 9,
Head 9 performs the next print scan.

FIG. 6 is a circuit diagram of the enlarged copying machine. Signal processing circuit 1
3 is controlled by the CPU, and comprehensively performs optical reading of document information, magnification magnification, memory to a predetermined address, printing control of the thermal head 9, and time width control of the above-mentioned energization time.

In response to a control signal supplied from the signal processing circuit 13, the clock pulse generation circuit 14 generates a clock pulse CLK having a predetermined pulse width. The image sensor 15 optically reads document information in synchronization with the clock pulse CLK, and this reading is performed for l scanning lines. The read signal Va between one scanning line is converted to a magnification conversion circuit 1.
6.

The magnification conversion circuit l6 sets a magnification for enlarged printing based on a control signal supplied from the signal processing circuit 13. The magnification is set in advance so that an A4 or B4 size document can be enlarged to Al or A2 size. And the selection of magnification is determined by the input circuit (not shown)
This is done by supplying a selection signal to the signal processing circuit 13 via the signal processing circuit 13.

The output signal vb of the magnification selection circuit 16 is sequentially stored in a predetermined address of the memory circuit 17, and the signal processing circuit 13 detects the completion of the storage operation for the scanning line. Next, according to the control signal supplied from the signal processing circuit 13, the output signal vb stored in the memory circuit l7, that is, the read signal is converted to the print signal Vc and sent to the thermal head operating circuit 18.
supplied to Note that the print signal Vc is not continuously supplied for one scanning line, but is divided into predetermined dots and supplied to the head operating circuit 18 at the same time.

As mentioned above, printing is performed by each of the thermal heads 9a to 9C, and the signal processing circuit 13
The energization control is performed by.

Therefore, even though enlarged printing is performed using the three thermal heads 9a to 9C, no density difference appears at the printing connection position, and the quality of print recording is improved.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above, and various modifications are possible.

For example, in the embodiment, there are three thermal heads 9a to 9a.
It explains the energization control of 9c, but basically 1
Similar control can be performed for each thermal head.

Furthermore, the present invention can be applied to various printers equipped with a thermal head,
It can be widely applied to copying machines and the like.

〔Effect of the invention〕

According to the thermal head control method according to the present invention, when energizing the thermal head, the energization time of the thermal head is controlled to be extended for a desired time from the start of printing signal supply, and after the elapse of the desired time, the thermal head is energized. Since the energization time is controlled in a steady state, when the thermal head is energized and the heat storage is low, the heat generation amount of the thermal head increases in accordance with the energization time width, but as the amount of heat storage increases, the heat generation amount of the thermal head increases. decreases in accordance with the energization time, and it is possible to equalize the density of images or prints recorded by the thermal head.

[Brief explanation of the drawing]

1 to 6 show embodiments and application examples of the present invention. FIG. 1 is an explanatory diagram showing the relationship between the arrangement of the thermal head and the energization time and concentration, and FIG. FIG. 3 is a schematic diagram of a thermal head showing another example of temperature control; FIG. 4 is a perspective view of an enlarged copying machine to which the present invention is applied; FIG. 6 is a circuit diagram of an enlarged copying machine, and FIG. 7 is an explanatory diagram showing the relationship between printing by a conventional thermal head and density. Symbols in the figure ■ - 1 Reading device W 2 1 Recording device 3 1 Insertion slot
5.12 - Discharge port 6--Heat-sensitive wire 7--Transport roller 8-One shaft 9a-9b--Thermal head 13-Signal processing circuit 16--Magnification conversion circuit 33-
- Heating element 34 - Substrate 35 - Temperature detection element T - Pulse signal period width t - Pulse signal rise width L1 - Interval for increasing energization 1 Fig. (A) Fig. 4 Fig. 5 Fig. 2 Figure 3 Figure/9°~9°

Claims (1)

[Claims] In a thermal head control method for supplying a print signal to a thermal head that scans on thermal paper and recording print on the thermal paper, the energization time of the thermal head is lengthened by a desired time width from the start of supply of the print signal. Thermal head control method to control