JPS6227994B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in the driving method of a thermal printer.

When continuous printing is performed with a conventional thermal printer, due to the accumulation of heat in the thermal print head (hereinafter referred to as the head), as the printing progresses sequentially from the first print to the second print, the temperature of the entire head is printed. This increases with operation, and has the disadvantage that the print density differs between the first and second prints, the second and third prints, or the print density differs from dot to dot within the same character.

As a method to minimize this drawback, a heat-sensitive resistance element (thermistor, etc.) is installed on the head to detect temperature changes in the head due to continuous printing, and the detection signal changes the printing time signal, or the detection signal drives the head. It has been proposed to change the current. However, this method requires the manufacture of a special head, that is, a head in which a heat-sensitive resistance element such as a thermistor is placed on the same surface as the heating element, making it difficult and expensive to manufacture. In addition, with this method, it is difficult to detect temperature changes at high speed due to the influence of the distance between the heat-sensitive element and the heat-generating element, the thermal conductivity of the substrate material on which both elements are placed, the thermal time constant, etc. It is impossible to control the printing time or drive current at high speed, and it is difficult to make the printing density uniform on the printing paper surface.

It is an object of the present invention to overcome these drawbacks and to provide an inexpensive thermal printer that can provide uniform printing density on the printing paper surface using only a simple circuit without using a special head.

An embodiment of the present invention will be described below with reference to the drawings.
FIG. 1 is a schematic diagram of the mechanism of the thermal printer of this embodiment. 1 and 2 are the side plates of the printer, 3 is the head,
4 is a shaft for sliding the head 3 left and right, and the head 3 is attached to the shaft 4 with enough room to slide. A sectional view thereof is shown in FIG. Reference numeral 5 denotes a motor which is a driving source for moving the head 3 left and right, and 6 a belt and pulley that transmit the movement of the motor 5 to the head 3 and move the head 3 left and right.

Figure 3 is an example of printing using the mechanism shown in Figure 1.
It is assumed that printing is performed from left to right, that is, from A to G in the figure, and the shaded area is the area that will be printed or heated, and the white area is the area that will not be printed, that is, the area that will not be heated. In addition, each of A to G is one printing unit by the head, and after printing in A, the head is moved to B by the motor 5 in the mechanism shown in FIG. 1 described above, and then printing is performed in B. Next, move the head to C in the same way and print at C. Thereafter, the same operation will be repeated to print from A to G. In d, the image is moved to e without printing.

FIG. 4 is a block diagram of an example of a conventional example.
CG is a print pulse generation circuit, AP is a head drive circuit that amplifies the CG signal, and SH is a thermal head incorporating a heat-sensitive resistance element. The temperature change sensed by the heat-sensitive resistance element is applied to the print pulse generation circuit CG or the head drive circuit AP, and the temperature is controlled. In the conventional example shown in FIG. 4, information on the temperature change of the head board from the heat-sensitive resistive element on the head is fed back to the drive system as described above, but as mentioned above, there is a large time delay, and as shown in FIG. The colors become darker in the order of A, B, and C, making it impossible to prevent uneven printing.

FIG. 5 is a block diagram of one embodiment of the present invention. CG is a printing pulse generation circuit, SK is an integration circuit that integrates the output signal of the printing pulse generation circuit CG, BB
is a differentiation circuit that differentiates the output signal of the print pulse generation circuit CG, CO is a comparison circuit that introduces the above-mentioned integral output and differential output and compares the integral output signal and the differential output signal, and AP is amplification of the output signal of the comparison circuit CO. The thermal head driving circuit SH is driven by the driving circuit AP, and is a thermal head that generates heat and prints.

FIG. 6 is a concrete example of a circuit implementing the block diagram of FIG. 5, and FIG. 7 is a timing chart thereof. In FIG. 6, OS is a one-shot multivibrator for generating printing pulses, S is an input terminal, and S is a negative output terminal. CO is a comparison circuit, A and B are input terminals, and Q is an output terminal. It is assumed that in this comparison circuit, Q=1 when the input voltage is A<B, and Q=0 when the input voltage A≧B.

Q ₁ is a PNP transistor, Q ₂ is an NPN transistor, R ₁ , R ₂ , R ₃ , R ₄ , R ₅ , R ₆ , R ₇ is a resistor, C ₁ ,
C ₂ and C ₃ are capacitors.

Also, a, b, d, e, f, g, and h indicate output lines and signal names, respectively. Here, signal a is a print start command pulse from a print pulse generation circuit, and signal h is a thermal head drive signal. Also transistor Q ₂
When turned on, the head generates heat and prints.

The pulse width Tb of the output signal b of the one-shot OS is determined by the time constant R ₁ ×C ₁ . Also, for convenience, the period of the print command pulse a is assumed to be 2×Tb. Transistor Q ₁ and resistor R ₂ constitute an inverter circuit I ₁ .
Transistor _Q1 is Tb with one-shot OS running
It will be ON during the time.

Resistor R ₃ and capacitor C ₂ constitute an integrating circuit SK. The charging time constant Te ₁ is determined by R ₃ × C ₂
Charging to C ₂ is performed when transistor Q ₂ is ON.

However, it is assumed that the input resistances of the input terminals A and B of the comparator circuit CO are sufficiently large compared to R ₃ , R ₄ , and R ₅ . Further, the resistor R ₄ is a discharge resistance for the capacitor C ₂ , and its time constant Te ₂ is determined by R ₄ ×C ₂ .

Resistor R ₅ and capacitor C ₃ constitute a differentiating circuit BB, and the differential signal f of the output signal d of the transistor Q ₁ is
occurs. The time constant Tf of this differentiator circuit BB is R ₅ ×
Determined by C ₃ .

In addition, the relationship between the charging time constant Te ₁ and the discharging time constant Te ₂ of the above-mentioned integrating circuit SK is such that Te ₁ < Te ₂ R ₃ ,
Set R ₄ and C ₂ .

The output signal l of the integrating circuit and the output signal f of the differentiating circuit are shown by solid lines and broken lines in FIG. 7, respectively.

As shown in FIG. 7, the printing command pulse a is a ₁ , a ₂ ,
When the pulses a ₃ arrive consecutively, the voltage of the signal e gradually increases along with the print command pulses a ₁ , a ₂ , and a ₃ because the print command pulse period=2×Tb and Te ₁ <Te ₂ . As a result, the high level time of the output signal g of the comparator circuit CO gradually becomes shorter as the voltage of the signal e increases. Further, as shown in FIG. 3D and F, when the printing command pulse is stopped at a point between _a3 and _a4 when no printing is performed, the voltage of the signal e gradually decreases due to the time constant _Te2 . As a result, after a pause in printing, the high level time of the output signal g of the comparator circuit CO becomes longer again.

Inverter _I2 , which consists of resistors _R6 , _R7 , and transistor _Q2 , is a thermal head drive circuit, and when printing continues, the ON time of _Q2 , that is, the low level time of signal h, gradually shortens, and printing stops again. If restarted after restarting, the
The ON time of _Q2 , that is, the low level time of h becomes longer. As a result, even in the case of the printing example shown in FIG. 3, it is possible to print without causing printing unevenness between A and G.

As is clear from the above explanation, the output of the differentiating circuit BB generates a predetermined level, which is used as a reference value for the comparator circuit CO, and this predetermined level can be generated by various other means and applied to the comparator circuit CO. It is clear that the voltage may be applied.

As described above, this invention does not require the use of a special thermal print head, but simply includes a simple circuit in the head drive system, allowing continuous printing or printing.
This eliminates uneven print density on the printing paper surface during single printing, and makes the density uniform.

Further, the present invention includes an integrating means for integrating a recorded signal and a differentiating means for differentiating the recorded signal, and a voltage value of an output signal generated by the integrating means and a voltage value generated by the differentiating means. Because it compares the voltage value of the output signal, the slope angle of the waveform differs greatly between the differential and integral waveforms.
The accuracy of signal level comparison can be increased.
Therefore, the present invention is capable of uniformizing the concentration with higher accuracy.

Furthermore, if an element for detecting the temperature around the printer is incorporated into this circuit, changes in print density due to the influence of the outside temperature or the temperature around the printer can be reduced, resulting in better print quality.

Further, the present invention can be applied to any of the methods of printing one dot or one segment at a time, printing one line at a time, and printing one character at a time.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a printer mechanism according to an embodiment of the present invention, and FIG. 2 is a schematic diagram of a mechanism of a head fixing section.
Figure 3 is a diagram showing an example of printing in the case of this embodiment;
5 is a block diagram of an example of the prior art, FIG. 5 is a block diagram of an embodiment of the present invention, FIG. 6 is a circuit diagram of a specific embodiment of the present invention, and FIG. 7 is the circuit of FIG. 6. This is a timing chart of each signal in the figure. SK... Integrating circuit, BB... Differentiating circuit, CO...
Comparison circuit.

Claims (1)

[Claims] 1. A thermal printer that records on recording paper by generating heat from a thermal head, comprising: an integrating means for integrating a recording signal; a differentiating means for differentiating the recording signal; a comparison means for comparing a voltage value of the output signal generated by the differentiating means with a voltage value of the output signal generated by the differentiating means; A thermal printer comprising: drive means for driving the thermal head based on the output signal of the comparison means that is output for a period smaller than the voltage value of the output signal.