JP2633243B2 - Thermal recording device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal recording apparatus that records an image or the like by a heating element that is selectively energized according to an image signal.

2. Description of the Related Art A thermal recording apparatus performs recording by heat of a heating element provided in a recording head. The heating element is selectively heated by the image signal and driven to generate heat. An image is recorded while repeating the energization of the selected heating element and the feeding movement of a recording medium such as thermal paper.

In particular, in a thermal recording apparatus used in a facsimile apparatus or the like, in order to record a received image at high speed, recording is performed in line units by a recording head in which a large number of heating elements are arranged in a main scanning line direction. .

In this type of thermal recording apparatus, the recording density or recording area on a recording medium such as thermal paper changes depending on the temperature when the heating element is driven to generate heat by energization, that is, the recording temperature. However, the recording temperature is affected by the surrounding temperature environment. For example, even if the heat generation amount of the heating element is the same, if the ambient temperature is low, the recording temperature becomes difficult to increase and the recording density becomes low. Conversely, if the ambient temperature is high, the recording temperature becomes too high and the recording density becomes high.

Therefore, in this type of conventional thermal recording apparatus, the ambient temperature of the heating element is detected using a temperature sensor such as a temperature resistance element, and the amount of heat generated by the heating element is variably controlled based on the detected temperature. A constant recording density and recording area were obtained regardless of the environment.

Problems to be Solved by the Invention However, according to such a configuration, it is effective against long-term changes in temperature environment such as those caused by environmental changes such as weather and air conditioning. It was not possible to cope with local temperature changes occurring during the process. For this reason, there has been a problem that unevenness in shading occurs in an image during recording and the image quality may be degraded.

The above problem occurs for the following reasons. That is, the detection response of the temperature sensor such as the temperature resistance element is slow. Even if the response of the temperature sensor itself is fast, the heat capacity of the mounting portion of the temperature sensor slows down the detection response. On the other hand, the recording temperature of the heating element greatly changes during recording due to heat generated from the heating element itself.
It has been difficult to detect and compensate for such a local change in the temperature environment with the above-described temperature sensor.

The present invention has been made in view of the above problems,
It is an object of the present invention to provide a thermal recording apparatus capable of keeping the recording temperature of a heating element constant during recording, thereby obtaining a high-quality recorded image without uneven density.

Means for Solving the Problems In order to solve the above problems, the present invention integrates the number of energized heating elements, and based on the integrated value, energizes the heating elements performed for each recording operation. Is variably controlled.

According to the present invention, a local change in the temperature environment caused by heat generation from the heating element itself is approximately compensated for by a change in the time for energizing the heating element. As a result, a change in the recording temperature during recording can be reduced, and a high-quality image with no uneven shading can be recorded.

Embodiment FIG. 1 shows a schematic configuration of a thermal recording apparatus according to an embodiment of the present invention.

In FIG. 1, reference numeral 1 denotes an input terminal for an image signal b. The image signal b is a binary signal composed of a signal "1" representing a black pixel and a signal "0" representing a white pixel, and is an external device (not shown).
Are input in series.

Reference numeral 2 denotes an input terminal for an image signal transfer clock d. The transfer clock d is input from the external device in synchronization with the image signal b.

Reference numeral 3 denotes an input terminal of the image signal valid period signal c. The image signal valid period signal c is input from the external device, and the image signal b
Is turned on (“1”) only while is input.

Reference numeral 4 denotes an output terminal for the image signal request signal a. The image signal request signal is output to the external device for each recording operation.

Reference numeral 5 denotes an integrating means for integrating the number of black pixel signals "1" in the image signal b. The integrating means 5 is constituted by using a counter for counting the total number of the black pixel signals "1".

Reference numeral 6 denotes a data converter, which converts the integrated value e of the integrating means 5 into time data f set in advance. The data conversion unit 6 is a ROM (non-volatile semiconductor storage device)
The data is converted by using a data table stored in advance in the data storage unit. The data table stores, for each integrated value e, the optimal time data f for obtaining a constant recording temperature.
Is stored in advance.

Reference numeral 7 denotes an energization time control unit that variably controls the time of energization i to the heating element 81 performed for each recording operation by the time data f. Vc indicates a power supply for the current supply.

Reference numeral 8 denotes a recording head, which can perform high-speed recording in line units by arranging a large number of heating elements 81 corresponding to the number of pixels for one line in the main scanning line direction. The recording head 8 has a built-in shift register 82 for holding an image signal for one line, and the presence or absence of energization of each heating element 81 is individually set according to the held content of each shift stage of the shift register 82. Is done. Then, only the heating element corresponding to the shift stage holding the black pixel signal “1” is selectively energized to thermally record the black pixel.

Reference numeral 9 denotes a control unit constituted by, for example, a microcomputer or the like, which generates the image signal request signal a to an external device and, based on an image signal valid section signal c input from the external device. , And controls the operation of the integrating means 5 and the energization time control unit 7.

FIG. 2 is a timing chart showing an operation example of the main part of the above-described thermal recording apparatus.

In FIG. 1 and FIG. 2, first, a clear signal j is given from the control section 9 to the integrating means 5 before recording of one image is started. Thereby, the integrated value of the integrating means 5 is reset to zero.

Thereafter, the control unit 9 outputs the image signal request signal a to the external device. When the request signal a is output, the valid section signal c
Is set to ON ("1"), and the image signal b for one line is input in series in synchronization with the transfer clock d. The input image signal b is input to a shift register 82 in the recording head 8. At this time, the number of black pixels signals n _B in the input image signal b is integrated by the integrating means 5.

When the input of the image signal b for one line is completed and the valid section signal c returns to off ("0"), the latch signal g is given from the control unit 9 to the energization time control unit 7, and the data conversion unit 6
Is output to the power-on time control unit 7. The time data f is converted from the integrated value e of the integrating means 5.

Immediately thereafter, the power supply start signal h is given from the control unit 9 to the power supply time control unit 7. Then, the energization control unit 7 energizes the heating element 81 corresponding to the black pixel signal “1” for a time T _ON from the energization start signal h to the time specified by the time data f.

The energized heating element 81 is driven to generate heat by an amount corresponding to the energizing time T _ON and reaches the recording temperature of the black pixel. As a result, the black pixel is thermally recorded at the position corresponding to the black pixel signal “1”.

As described above, an image for one line is recorded in the main scanning direction. Thereafter, the relative position between the recording head 8 and the recording medium is pitch-shifted by one pixel in the sub-scanning direction, and recording of the next line is performed. At this time, the integrated value e is carried over without being reset. The integrated value e is accumulated every time recording of one line is performed until recording of all lines is completed.

One image is recorded while repeating the above operation. During this recording, the temperature environment of the heating element 81 locally changes due to the heat generated by the heating element 81 itself. Accordingly, a difference occurs in how the recording temperature rises with respect to the energization time T _ON . The recording temperature is more likely to increase as the total number of the heating elements 81 that are energized and driven to generate heat increases. That is, the recording temperature of the heating element 81 during recording tends to gradually increase in accordance with the integrated value e of the number of the heating elements 81 that are energized.

Here, the time data f output from the data converter 6 for each integrated value e is set to a value that can reduce the amount of heat generated by an increase in the recording temperature that is expected to occur according to the integrated value e. In advance, the change in the local temperature environment caused by the heat generated from the heating element 81 itself is approximately compensated by the change in the energization time T _ON . As a result, a change in the recording temperature during recording can be reduced, and a high-quality image with no uneven shading can be recorded.

The integrating means 5 may be constituted by, for example, a circuit that performs an analog integration of the logic level of the black pixel signal “1” and a D / A converter that converts the analog integrated value into a digital value. The present invention is also applicable to a so-called serial type thermal recording apparatus in which a plurality of heating elements are arranged in the sub-scanning direction.

Advantages of the Invention As is clear from the above description, the present invention integrates the number of energized heating elements and calculates one based on the integrated value.
With the configuration in which the energization time to the heating element performed for each recording operation is variably controlled, a change in a local temperature environment caused by heat generation from the heating element itself is approximately compensated for by a change in the energization time. In addition, there is an effect that a change in the recording temperature during recording can be reduced, and a high-quality image without density unevenness can be recorded.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a schematic configuration of a thermal recording apparatus according to an embodiment of the present invention, and FIG. 2 is a timing chart showing an operation example of the main part. 1 ... input terminal of image signal b, 5 ... integrating means, 6 ... data conversion unit, 7 ... energization time control unit, 8 ... recording head, 81 ... heating element, 82 ... shift register, e ... Integrated value, f... Time data, i.

Claims (1)

(57) [Claims] 1. A recording head in which a heating element corresponding to the number of pixels for one line is provided, and an integration in which the number of elements energized to the heating element is sequentially integrated until recording of a predetermined unit image is completed. Means, a data conversion unit for converting the data into preset time data corresponding to the integrated value of the integrating means, and an energizing means for variably controlling the energizing time to the heating element by the time data for each recording of one line. A thermal recording device comprising a time control unit.