JPH0620613Y2 - Head drive circuit for thermal transfer color printer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to a head drive circuit for a thermal transfer color printer, and more particularly to a head drive circuit for a thermal transfer color printer in which the difference in print density is reduced.

[Prior Art] Conventionally, as a thermal transfer type color printer, a transfer film in which three colors of yellow (Y), magenta (M), and cyan (C) are separately applied is used, and a transfer target paper is reciprocated three times. A method is known in which a Y color → M color → C color is overlaid and transferred. FIG. 5 is a diagram showing a printing process of a color printer of this type. In FIG. 5, 1 is a transfer sheet, Hp is a position of a thermal head, and SP is a symbol.
Indicates a transfer start position, reference numeral FP indicates a transfer end position, and reference numerals A _{1 to} A ₅ indicate the conveyance direction of the transfer target paper 1.

By the way, as a method of controlling the print density in the thermal transfer color printer of this type, the temperature of the thermal head is detected before printing of each color, and the head drive energy of the thermal head is controlled based on the detection result.

[Problems to be Solved by the Invention] By the way, in the above-mentioned thermal transfer type color printer,
Since the temperature detecting element (for example, thermistor) that detects the temperature of the thermal head is attached to the heat sink attached to the thermal head, the temperature of the heating element of the thermal head is not directly transmitted to the temperature detecting element, but is passed through the heat sink. Therefore, the temperature detected by the temperature detecting element and the actual temperature of the heating element are somewhat different from each other. Therefore, there are the following problems. That is, the transfer paper 1 is returned to the transfer start position SP for performing the next transfer (magenta) after the transfer of yellow, for example, but during this return, the accumulated heat of the heating element is radiated through the heat sink. It In this case, since the heat radiated from the heating element is gradually transmitted through the heat sink, when the transfer target sheet 1 reaches the transfer start position SP, the temperature of the heating element is lower than the temperature of the outer wall surface of the heat sink. Becomes Therefore, the temperature of the heating element detected by the temperature detecting element when magenta is transferred is higher than the actual temperature of the heating element. Based on this value, the head drive energy value to be supplied to the heating element when transferring magenta is determined. Therefore, this energy value is lower than the energy value required to obtain optimum print quality,
The print density becomes lighter at the beginning of the page on which magenta is transferred. On the other hand, as the transfer progresses, the heating element accumulates heat, so the print density becomes higher at the end of the page. Also,
In particular, when the number of dots to be printed is large, “fading” occurs at the beginning of the page and “tailing” occurs at the end of the page.

Although the above-mentioned problem has been described in the case where magenta is transferred to the transfer target paper 1, the same applies to the case where yellow and cyan are transferred.

The present invention has been made in view of such a background, and its purpose is to eliminate the "blurring" at the start of printing of each color and reduce the print density difference within one page, and the head drive of the thermal transfer type color printer. To provide a circuit.

[Means for Solving the Problems] The temperature of the thermal head is detected in the head drive circuit of the thermal transfer type color printer that detects the temperature of the thermal head and controls the energy supplied to the thermal head based on this temperature. A first detection unit, a second detection unit that detects an ambient environmental temperature, and a third detection unit that obtains a difference between a detection result of the first detection unit and a detection result of the second detection unit. Storage means for storing preheating energy data corresponding to an energy value emitted from the thermal head during a non-transfer period during which the transfer target sheet returns from the transfer end position to the transfer start position; During the transfer period, preheating energy data corresponding to the detection result of the third detecting means is read from the storage means, and the read data is indicated. Control means for supplying the thermal energy to the thermal head.

[Operation] According to the above configuration, the temperature of the thermal head and the ambient environmental temperature are detected, and the preheating energy value corresponding to the difference between these detection results is supplied within the non-transfer period of the thermal head, Since it is preheated, the beginning of printing does not become lighter or faint. In other words, by preheating the thermal head during the transfer period of the thermal head,
The temperature of the heating element of the thermal head when starting printing,
Since there is no difference in temperature from the temperature detected by the temperature detecting element attached to the heat sink of the heating element, the temperature of the heating element itself can be detected. As a result, the head drive energy value that provides the optimum print density when printing each color is obtained.

[Embodiment] An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing the electrical construction of an embodiment of the present invention.

In the figure, 1 is a print data memory in which a dot-converted print data DB is stored. Reference numeral 2 is a control unit having an MPU (microprocessing unit), a program memory 2a, a work memory 2b, a printing energy data memory 2c, a first preheating data memory 2d, and a second preheating data memory 2e. This control unit 2
It has a function of reading the print data DB stored in the print data memory 1 and a function of inputting and outputting control signals and data to various circuits described later.

A thermal head 3 is composed of a shift register circuit 4, a latch circuit 5, drivers 6a to 6d, and a heating element 7. The shift register circuit 4 is a serial-in parallel-out shift register, and based on the clock signal CLK supplied from the control unit 2, the control unit 2
The print data DB output from is read and output to the latch circuit 5. The latch circuit 5 reads the output of the shift register circuit 4 based on the latch signal DR output from the control unit 2 and outputs it to the drivers 6a to 6d. The driver 6a is composed of NAND gates Ga _{1 to} Gan. Similarly driver 6b NAND gate Gb ₁ ~Gbn, driver 6c NAND gate Gc ₁ ~Gcn, the driver 6d is composed of NAND gates Gd ₁ ~Gdn. Further, each of the first input terminals of the NAND gates Ga _{1 to} Gan of the driver 6 a is connected to the output terminal of the latch circuit 5, and the second input terminals thereof are commonly connected to each other and connected to the timer circuit 12. It is connected to the first output end. Similarly, the first input terminals of the NAND gates of the drivers 6b to 6d are connected to the output terminal of the latch circuit 5, and the second input terminals thereof are commonly connected, and the second to fourth outputs of the timer circuit 12 are respectively connected. Connected to the end. The output terminals of the NAND gates Ga _{1 to} Gan of the driver 6 a are connected to the heating elements THa ₁ to THa _{1 of the} heating element 7.
It is connected to one end of THan. Similarly, the driver 6b
The NAND gates of 6d are also connected to one end of each heating element of the heating element 7. The other ends of the heating elements THa _{1 to} THdn are commonly connected to each other and connected to the positive power source V. In this case, a heat sink (not shown) is attached to the heating element 7 in order to improve heat dissipation.

Next, 8 is a temperature detecting element for detecting the temperature of the heating element 7, which is attached in close contact with the heat sink of the heating element 7. Reference numeral 9 denotes a temperature detecting element that detects the ambient environmental temperature, and is attached to the case (not shown) surface of the printer body. The detection signals output from these temperature detection elements 8 and 9 are supplied to the analog multiplexer 10, respectively. The analog multiplexer 10 has an input end for two channels, and one of the detection signals output from the above-mentioned temperature detection elements 8 and 9 based on the channel select signal CS supplied to its select terminal. Is selected and supplied to the A / D (analog / digital) converter 11. The A / D converter 11 is a detection signal (analog value) output from the temperature detection elements 8 and 9.
Is sequentially converted into a digital signal and supplied to the control unit 2. Here, the converted detection signal output from the temperature detection element 8 is referred to as temperature data TM, and the converted detection signal output from the temperature detection element 9 is referred to as temperature data TE. The timer circuit 12 receives the signal P from the control unit 2.
When P is supplied, the signals RT _{1 to} R having pulse widths corresponding to the print energy data RE, the first preheat data ED, or the second preheat data EDD supplied from the control unit 2 are supplied.
Of T ₄ occurs, and sequentially output to each block of the driver 6a-6b.

Next, the operation of this circuit will be described with reference to the flowchart of FIG. In this flowchart, the transfer process from steps S1 to S4 is shown in FIG.

First, when the power is turned on, the transfer film 1 is moved to the transfer start position SP while the transfer film 1 is cued to the yellow position. During this period, the control unit 2 preheats the heating element 7 in step S1. That is, first, the data of ALL “1” is written in the shift register circuit 4. Next, read the temperature data TM, TE,
A temperature difference ΔT between the temperature data TM and TE is calculated.
Then, based on the temperature difference ΔT, the preheating energy data ED preset in the first preheating data memory 2d is read from the memory 2d. This data ED is supplied to the timer circuit 12. In this case, the preheating energy data ED is an energy value at which the temperature of the heating element 7 does not cause printing, which is previously obtained by an experiment, and is stored in the first preheating data memory 2d by a table.

When the preheating energy data ED is supplied to the timer circuit 12, the control section 2 then supplies the signal PP to the timer circuit 12. As a result, the signal RT _{1 of the} pulse width corresponding to the preheating energy data ED is output from the timer circuit 12.
Up to RT ₄ are sequentially and repeatedly supplied to the drivers 6a to 6d at predetermined intervals. Then, the drivers 6a to 6d
A current flows through each of the heating elements THa _{1 to} THdn due to the "1" level signal output from the latch circuit 5 and the "1" level signal already output from the latch circuit 5. As a result, the heating element 7 is preheated.

Next, the control unit 2 performs yellow printing in step S2. That is, the print data DB is read from the print data memory 1 and this data DB is written to the shift register circuit 4. Next, the temperature data TM is read, based on the temperature data TM, the printing energy data RE preset in the printing energy data memory 2c is read from the memory 2c and supplied to the timer circuit 12. In this case, the printing energy data RE is an energy value for which the temperature of the heating element 7 is the optimum printing density, which is obtained in advance by an experiment, and is stored in the printing energy data memory 2c by a table.

As a result, the transfer sheet 1 and the yellow transfer film are conveyed, and the yellow transfer is performed on the transfer sheet 1.

Next, when the transfer target sheet 1 reaches the transfer end position FP,
The control unit 2 preheats the heating element 7 in step S3. That is, the ALL in the shift register circuit 4
Write the data of "1". Next, temperature data TM,
TE is read and the temperature difference ΔT between these temperature data TM and TE is calculated. Then, based on this temperature difference ΔT,
The preheating energy data EDD preset in the second preheating data memory 2e is read from the memory 2e, and this data EDD is supplied to the timer circuit 12. In this case, the preheating energy data EDD is the transferred paper 1
In consideration of the energy value radiated from the heating element 7 while returning from the transfer end position FP to the transfer start position SP, the energy value at which the temperature of the heating element 7 becomes a temperature at which printing does not occur is previously obtained by an experiment. , And is stored in the second preheating data memory 2e by a table.

Then, the preheating energy data EDD is transferred to the timer circuit 12
Then, the control unit 2 supplies the signal PP to the timer circuit 12. As a result, the signal R of the pulse width corresponding to the preheating energy data EDD is output from the timer circuit 12.
T _{1 to} RT ₄ are sequentially and repeatedly supplied to the drivers 6a to 6d at predetermined intervals. And this driver 6a-
A current flows through each of the heating elements THa _{1 to} THdn by the "1" level signal output from 6d and the "1" level signal already output from the latch circuit 5. As a result, the heating element 7 is preheated. In this case, FIG. 4 shows the states of the signals RT _{1 to} RT ₄ which are sequentially and repeatedly supplied to the drivers 6a to 6d as the transfer target sheet 1 is conveyed. In this figure, Sep1～Sep6 · · · represents the step of conveying the transfer sheet 1, _{T 1} is preheated repetition time, _{T 2}
Indicates the preheating time.

Next, when the transfer target sheet 1 reaches the transfer start position SP,
The control unit 2 prints magenta in step S4. In this case, the same operation as that performed in step S2 is performed. Next, the control part 2 preheats the heating element 7 in step S5. Then, in step S6, cyan printing is performed. In this case, the operations performed in steps S5 and 6 described above are the same as the operations performed in steps S3 and S4.

As described above, according to the present invention, the non-transfer period, that is, while the transfer target sheet before printing yellow is conveyed to the transfer start position, and the transfer target sheet 1 before printing magenta and cyan is at the transfer start position. While being rewound to SP, preheating energy is supplied to the heating element 7 to prevent the temperature of the heating element 7 from decreasing during this period, so that the detection signal detected by the temperature detecting element 8 matches the temperature of the heating element 7. To do. As a result, the beginning of transfer does not become thin or is not blurred, and as a result, uniform print quality can be obtained.

In the embodiment of the present invention, the energy value supplied to the heating element 7 is controlled by changing the energization time (depending on the pulse width), but the voltage value may be changed. Further, in the embodiment of the present invention, a separate table for storing energy data for preheating the heating element 7 is used, but when these are combined into one and supplied to the heating element 7, a predetermined constant is multiplied. You may make it convert a data value.

As described above, according to the present invention, in the head drive circuit of the thermal transfer type color printer which detects the temperature of the thermal head and controls the energy supplied to the thermal head based on this temperature, The first detection means for detecting the temperature of the head, the second detection means for detecting the ambient environmental temperature, the difference between the detection result of the first detection means and the detection result of the second detection means, Third to seek
Detecting means, a storage means for storing preheating energy data corresponding to an energy value diverged from the thermal head during a non-transfer period during which the transfer target sheet returns from the transfer end position to the transfer start position, and the thermal head. In the non-transfer period, the preheating energy data corresponding to the detection result of the third detecting means is read from the storage means, and the energy indicated by the read data is supplied to the thermal head. By eliminating "blurring" at the start of printing, it is possible to reduce the density difference within one page.

[Brief description of drawings]

FIG. 1 is a block diagram showing the electrical construction of an embodiment of the present invention, FIG. 2 is a flow chart for explaining the operation of the same embodiment, and FIG. 3 is a printing process for supplementing the explanation of the flow chart. 4 and 5 are waveform charts showing preheating energy data of the same embodiment, and FIG. 5 is a diagram showing a printing process of a conventional thermal transfer color printer. 2 ... Control unit (having third detection means and control means),
2d ... 1st preheating data memory, 2e ... 2nd preheating data memory (2d and 2e are storage means), 3 ... Thermal head, 8 ... Temperature detector (1st detection means), 9 ...
... Temperature detector (second detection means).

Claims (1)

[Scope of utility model registration request] 1. A head drive circuit of a thermal transfer type color printer which detects (a) the temperature of a thermal head and controls the energy supplied to the thermal head based on this temperature. (B) Detects the temperature of the thermal head. A first detection means for: (c) a second detection means for detecting an ambient environmental temperature; (d) a difference between the detection result of the first detection means and the detection result of the second detection means. And (e) preheat energy data corresponding to the energy value radiated from the thermal head is stored during the non-transfer period during which the transfer target sheet returns from the transfer end position to the transfer start position. And (f) reading out preheating energy data corresponding to the detection result of the third detecting means from the storage means during the non-transfer period of the thermal head, Head drive circuit of the thermal transfer type color printer, characterized in that the energy indicated by the read data is and control means for supplying to said thermal head.