JP2729511B2 - Thermal head control method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal head control method suitable for use in an image recording apparatus configured to record characters, graphics, images, and the like using a thermal head. More particularly, 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]

Some image recording apparatuses such as printing printers and image printers use a thermal head as recording means. The thermal head has a structure in which a large number of heating resistance elements (hereinafter referred to as heating elements) are adhered to a ceramic substrate or an aluminum base formed in a flat plate shape.

When image recording is performed, an arrow A shown in FIG.
As shown by the arrow, the thermal head 32 is scanned on the thermal paper 31 and, at the same time, a large number of heating elements are energized based on a print signal or an image signal to record characters, graphics, etc. on the thermal paper 31.

[Problems to be solved by the invention]

Although the thermal head 32 generates heat almost in proportion to the energizing time, the heat generation amount is not saturated in the initial stage of driving, so that a sufficient heat generation amount cannot be obtained, resulting in poor coloring at the time of printing.

Therefore, the density of the image recorded on the thermal paper 31 changes from a low density to a high density as shown in FIG. 7 (B) due to the unsaturated heat and heat storage of the heating element. Does not have a uniform concentration.

On the other hand, the density change can be reduced by increasing the amount of power of the heating element for printing in one line and generating heat in the saturation region. However, in this case, the power consumption becomes large and not only shortens the life of the thermal head but also
Problems such as a decrease in recording speed occur.

In particular, in a printer in which, for example, three thermal heads 32 are arranged at regular intervals as shown by virtual lines in FIG. At the connection position of the image recorded by the thermal head 32, as shown in FIG. 7 (B), a remarkable density difference appears, and a high quality image cannot be obtained.

The present invention has been made to solve the above problems,
An object of the present invention is to provide a thermal head control method capable of reducing density unevenness during image recording.

[Means and actions for solving the problem]

The object according to the present invention is to print and record on the thermal paper by scanning a plurality of thermal heads arranged at regular intervals in the width direction of the thermal paper at the constant intervals in the width direction of the thermal paper. In the thermal head control method, a print signal is supplied to each of the thermal heads at the start of scanning of each of the thermal heads, and a desired time width from the start of scanning and the energization time of each of the thermal heads are increased, This is achieved by a thermal head control method that controls the energizing time to return to a steady state after each of the thermal heads scans the desired time width.

That is, the supply time of the print signal is controlled to be long for a desired time from the start of the supply of the print signal, and after the desired time has elapsed, the time width of the print signal is controlled to a steady state. As a result, before the heat is stored in the thermal head, the recording density is increased by a print signal that sets a large amount of heat generation, and after a desired time elapses, image recording is performed by the heat storage and heat generated from the thermal head. Can be equalized.

[Embodiments] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the description of this embodiment, a method of controlling the thermal head will be described with reference to FIGS. 1 to 3, and then, with reference to FIGS. explain.

As shown in FIG. 1A, three thermal heads 9a, 9b, 9c are arranged on the recording paper 6 at equal intervals L. The recording paper 6 is configured to be conveyed by a predetermined distance (main scanning) in the direction of arrow B every time the thermal heads 9a to 9c perform one scan (sub-scan) in the direction of arrow A and perform image recording. .

In this embodiment, as shown in FIG. 1B, the thermal heads 9a to 9b are arranged at a predetermined interval L1, for example, about 10 mm from the position P1 at which the thermal heads 9a to 9b start sub-scanning. Control is performed so as to increase the energizing time of 9c, and the energizing time is controlled to a steady state after scanning about 10 mm. The control of the power supply time, in other words, the control of the power supply amount, will be described later with reference to FIG.

The energization of each of the thermal heads 9a to 9c as described above is performed based on a print signal described later. Therefore, the energization control is to control the energization time of each of the thermal heads 9a to 9c to be large at the start of the supply of the print signal,
From the point in time when the recording at the predetermined interval L1 ends, the power supply is controlled to the steady state.

By performing such energization control, the amount of heat generated by each of the thermal heads 9a to 9c increases during L1, and after the end of recording during L1, recording is performed using heat generated by steady energization and heat storage. As a result, the density of the recorded image is equalized as shown in FIG. 1C, and in particular, the density difference at the print boundary position P1 between the two thermal heads can be reduced. According to the conventional control, a density difference as shown by a virtual line in FIG. 1 (C) appears. However, by controlling the energization of each of the thermal heads 9a to 9c as described above, the density difference is reduced. Can be reduced.

The interval L1 is set according to each of the thermal heads 9a to 9c.
Can be arbitrarily changed depending on the number of heating elements, the properties of the recording paper 6, and the like, and are not limited to the above-mentioned about 10 mm.

Also, if the life of the thermal heads 9a to 9c is not affected,
As shown by the dotted line in FIG. 1, it is possible to make the concentration uniform by keeping the amount of change in the energization time constant.

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

A pulse signal V1 as shown in FIG. 2 is supplied to the heating elements of each of the thermal heads 9a to 9c in response to the print signal, and the energization time is controlled by the rise time width t of the pulse signal V1. Done. Now, suppose that the pulse signal
If the cycle width T of V1 is set to 1.8 ms and the rising time width t is controlled to, for example, 1.5 ms while scanning the interval L1, the amount of heat generated corresponding to the time width t increases. Also, the interval L1
If the time width t is controlled to be as short as about 0.9 ms at the end of the recording, the amount of generated heat will be reduced, and the above-described density equalization will be performed.

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

FIG. 3 shows a cross-sectional structure of each of the thermal heads 9a to 9c.
It is mounted on the top by bonding or the like. A temperature detecting element 35 such as a thermistor is provided on a part of the ceramic substrate 34, and the rising time t of the pulse signal V1 is controlled by the temperature detecting signal V2.

According to the thermal head control method described above,
Since the heat generation of the thermal head can be controlled in accordance with the heat storage amount, the recording density can be equalized as shown in FIG.

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

In addition, although the energization time after returning the energization time to the steady state is a constant level, the heat generation amount in the steady state can be adjusted by uniformly increasing and decreasing the energization time level in the steady state over the entire range, The color density of the thermal paper 6 can be adjusted.

FIG. 4 is a perspective view of an enlarged copying machine for implementing the method of controlling a thermal head according to the present invention. This enlarged copier is
For example, this is an apparatus for enlarging and copying an A4 size original to an A1 size, and includes an original reading device 1 and a recording device 2.

The reading device 1 includes an image sensor that scans a document in the width direction and reads an 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 accommodates 594 mm wide thermal paper 6 (corresponding to the recording paper) wound in a roll shape, and includes three thermal heads that perform print scanning in the width direction (sub-scanning direction) of the thermal paper 6. Have. Three thermal heads within the effective main scanning width
It has 64 dots and is arranged at equal intervals on the same scanning line, and each thermal head simultaneously scans the thermal paper 6 at equal intervals to print one line across the width direction. Then, the thermal paper 6 on which the predetermined recording has been performed is discharged from the discharge port 12.

FIG. 5 is a schematic configuration diagram of the recording apparatus 2. The heat-sensitive paper 6 wound in a roll shape is transported by transport rollers 7 formed using chloroprene rubber, polyacetal, or the like. The thermal head 9 is fixed to a base 10 and a platen 11
The printing is performed by scanning the thermal paper 6 in contact with the thermal paper 6 supported by the printer. When one print scan over the entire width of the thermal paper 6 is completed, the head 9 starts a return operation to the scanning start position, and at the same time, a motor (not shown) for rotating and driving the transport roller 7 operates to remove the thermal paper 6. Head 9 in the direction indicated by arrow D
The conveying roller 7 is driven to rotate so as to convey the main scanning amount. After the thermal paper 6 has been conveyed by the main scanning of the head 9, the head 9 performs the next printing scan.

FIG. 6 is a circuit diagram of the enlarged copying machine. Signal processing circuit
Reference numeral 13 denotes a CPU, which is configured to optically read document information, enlarge magnification, store memory at a predetermined address, and a thermal head 9.
Print control, and the above-described time width control of the energization time are comprehensively performed.

The clock pulse generating circuit 14 generates a clock pulse CLK having a predetermined pulse width according to a control signal supplied from the signal processing circuit 13. The image sensor 15 optically reads the document information in synchronization with the clock pulse CLK, and the reading is performed for one scan line. The read signal Va for one scan line is supplied to the magnification conversion circuit 16.

The magnification conversion circuit 16 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 an A1 or A2 size. The selection of the magnification is performed by supplying a selection signal to the signal processing circuit 13 via an input circuit (not shown).

The output signal Vb of the magnification selection circuit 16 is sequentially stored at a predetermined address of the memory circuit 17, and the end of the storage operation for one scanning line is detected by the signal processing circuit 13. Next, the memory circuit is controlled by a control signal supplied from the signal processing circuit 13.
The output signal Vb stored in the memory 17, ie, the read signal, is supplied to the thermal head operating circuit 18 as the print signal Vc. The print signal Vc is not supplied continuously for one scan line, but is supplied to the head operating circuit 18 at the same time by dividing a predetermined dot.

As described above, printing is performed by the thermal heads 9a to 9c, and the energization control is performed by the signal processing circuit 13 during printing and recording. Therefore, even though the enlarged print is performed using the three thermal heads 9a to 9c, no density difference appears at the print 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 above embodiment, three thermal heads 9a to
Although the energization control of 9c has been described, basically the same control can be performed for one thermal head.

Further, the present invention can be widely applied to various printers, copiers and the like having a thermal head.

〔The invention's effect〕

According to the thermal head control method of the present invention, when energizing the thermal head, a desired time from the start of supply of a print signal, while controlling so as to extend the energizing time of the thermal head, and after the elapse of the desired time, Since the energization time is controlled to a steady state, the amount of heat generated by the thermal head increases in accordance with the energization time width while the heat is being supplied to the thermal head and heat storage is small, while the amount of heat generated by the thermal head increases as the amount of heat storage increases. Is reduced in accordance with the energizing time, and the density of the image or print recorded by the thermal head can be equalized.

[Brief description of the drawings]

1 to 6 show an embodiment and an application example of the present invention. FIG. 1 is an explanatory diagram showing the relationship between the arrangement of the thermal head and the energizing time and density, 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 copier to which the present invention is applied, FIG. FIG. 6 is a schematic diagram of a recording apparatus, FIG. 6 is a circuit diagram of an enlarged copier, and FIG. 7 is an explanatory diagram showing a relationship between recording by a conventional thermal head and density. Reference numeral 1 in the drawing: reading device, 2: recording device 3, insertion port, 5, 12, discharge port 6, thermal paper, transport roller 8, shafts 9a to 9b, thermal head 13 …………………………………………………………………………………………… ·················································································· Interval

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-60-67178 (JP, A) JP-A-60-42073 (JP, A) JP-A-61-160257 (JP, A) JP-A-56-167 161182 (JP, A) JP-A-2-32871 (JP, A)

Claims (2)

(57) [Claims] A plurality of thermal heads arranged at regular intervals in the width direction of the thermal paper to scan the thermal paper at a constant interval in the width direction of the thermal paper, thereby performing print recording on the thermal paper. In the method, a print signal is supplied to each of the thermal heads at the start of scanning of each of the thermal heads, and a desired time width from the start of scanning, and the energization time of each of the thermal heads are increased, so that each of the thermal heads A thermal head control method for controlling the energization time to return to a steady state after each of the desired time width scans. A plurality of thermal heads arranged at regular intervals in the width direction of the thermal paper to control printing by printing on the thermal paper by scanning at a constant interval in the width direction of the thermal paper; In the method, a printing signal is supplied to each of the thermal heads at the start of scanning of each of the thermal heads, and the amount of change in the energization time of each of the thermal heads is changed from the start of scanning to the end of scanning of each of the thermal heads. A thermal head control method that controls the temperature to be constant.