JPH0117469B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for driving a thermal head for printing in halftone density.

FIG. 1 shows the conventional thermal head drive timing. In FIG. 1a, T is the shortest repetition cycle of the thermal head, during which time the head is driven and cooled to print one dot, and T is constant. t _o , t _n , and to _oa divide the density of thermal paper into n gradations, and the nth, mth, (n-
This is the head driving time for printing at the a)th density. In Fig. 1b, θ _o , θ _n , and θ _oa are the head temperatures when printing at the nth, mth, and (na)th densities of n gradations, and θ ₀ is the head temperature when printing on ka-netsu paper. head temperature. Figure 1b is drawn from the time when the head temperature has reached θ ₀ . After driving t _o , the head temperature rises to θ _o , and is then cooled down, but before it falls to θ ₀ , the head temperature rises to θ _n during the subsequent head driving time t _{n (1)} . After rising to θ _n , the head temperature drops to below θ ₀ . With the subsequent head driving time t _{n (2)} (t _{n (1)} < t _{n (2)} ), the head temperature rises to θ _n . The reason why the head temperatures are the same even though t _{n (1)} and t _{n (2)} are not equal is because the head temperatures of the dots before the dot to be printed are different. In other words, in order to obtain an appropriate head temperature, that is, recording density, depending on the image signal information, the head driving time t of the dot to be printed must be determined based on the information of the image signal one dot before.
need to be controlled.

The present invention focuses on this point, and aims to perform halftone density printing with simpler control to obtain more appropriate printing density.

This will be explained below along with examples. In FIG. 2, T is the shortest repetition cycle of the thermal head, and t ₁ (Y) is the head driving time required to raise the head temperature to θ ₁ (however, this t ₁ (Y)
varies depending on the initial temperature of the head),
At t ₂ ′, t ₃ ′, ...t _o ′, the head temperature is θ ₁ →θ ₂ , θ ₂ →θ ₃
,
This is the head drive time required to increase from θ _o-1 → θ _o .

Note that θ ₁ , θ ₂ , ... θ _o are the head temperatures necessary to obtain the density of each gradation in the head drive repetition period T, and θ _o is the head temperature at which the density of the thermal paper becomes saturated. It is.

Since the voltage applied to the head is constant, the energy required for the head temperature to rise from θ ₁ → θ ₂ , θ ₂ → θ ₃ ...θ _o-1 → θ _o is determined by the head driving time.
Depends on t ₂ ′, t ₃ ′, ...t _o ′. Therefore, for example, the driving time t _n required to raise the head temperature to θ _n (m<n) is as follows.

t _n = t ₁ (Y) + t (m) However, here t (m) = t ₂ ′ + t ₃ ′ +…+t _n ′,
Further, t ₁ (Y) is the driving time required to raise the head to θ ₁ .

By setting such a driving time, an appropriate print density can be obtained. In other words, control of t(m) is possible based on the print information that is to be printed in its entirety.

Next, regarding the head drive time t ₁ (Y), in the embodiment shown in the head drive time chart in FIG. 3, the cooling start time τ ₀ is constant for each dot printing, and the head temperature at that time is can be estimated from the printed information of the previous one dot (θ _o in the case of τ ₀ ). Also, the cooling time (τ ₁ - τ ₀ ) is determined by the driving time t _{(o -1), which is determined by the print information of the dot that is about to be printed (in the figure, the recording density is θ o-1} at the head temperature).
The head driving time t ₁ (Y) for raising the head temperature from the cooling end time τ ₁ to θ ₁ is removed from the repetition period T. That is, the cooling time and the head temperature at the end of cooling are substantially determined by the head temperature at the start of cooling.

Therefore, it is possible to obtain an appropriate head driving time t ₁ (Y) in advance from the above information, and use it as
It can be stored in ROM. In other words,
If the print information of the previous dot is n ₁ and the print information to be printed now is n ₂ (however, n ₁ and n ₂ are both integers),
The head driving time t ₁ (Y) is t ₁ (Y)=t ₁ (n ₁ , n ₂ )On ₁ , n ₂ n, and in this embodiment, the head driving time
By having (n+1) ^two values of t ₁ (Y) in advance, it is possible to cover the recording of all printing densities.

Further, in the embodiment shown in FIG. 4, in the head drive repetition period T, the head drive time t ₁ (Y)
Since the point in time (point B shown in FIG. 2) at which the head temperature ends (point B in FIG. 2) is constant during each cycle, for example, the head temperature θ ₁
The _head drive time t(m) required to _raise the _{head temperature} from Yes, from the end of the head drive repetition period T (point A shown in Figure 2), (t _o '+t' _o-1 +
...+t' _n+1 ) earlier, the head drive in that cycle ends. Regarding the control of the head drive time t ₁ (Y) in this embodiment, the point at which the head drive time t ₁ (Y) ends (the second
Point B in the figure) is constant, and since the print information of the previous dot allows us to know the head temperature at the end of head driving and the start time of cooling for the previous dot, the cooling time can be estimated.

Therefore, as in the first embodiment, an appropriate head driving time t ₁ (Y) can be obtained in advance from the above information, and it can be stored in the ROM. In other words, if the previous print information is n ₁ ,
The head drive time t ₁ (Y) is as follows.

t ₁ (Y)=t ₁ (n ₁ ) where On ₁ n and n ₁ are integers.

Therefore, in this embodiment, the head driving time t ₁ (Y) has (n+1) values in advance, so that recording of all print densities can be covered. In this way, the embodiment described in conjunction with FIG. 4 is compared with the embodiment described in conjunction with FIG.
The memory capacity required for controlling the head drive time t ₁ (Y) is small.

FIG. 5 is a block diagram showing a circuit to which the thermal head driving method according to the present invention is applied. Reference numeral 501 reads and writes the print information of the previous one dot and the print information to be printed to and from the RAM 502, and This is a data control unit that determines the address of information read from the ROM 503. 502 is a RAM for temporarily storing the print information of the previous one dot or the print information of the dot to be printed now;
503 is a ROM that stores information on an appropriate head drive time t in advance; 504 is a head drive time control unit that appropriately controls the head drive time based on the information in the ROM 503; 505 is a head drive circuit; 506
507 is a thermal head, and 507 is a power supply.

Next, the operation of this embodiment will be explained. Input data obtained by A/D converting the image signal is input to the data control unit 501, and the data is stored in the RAM 502, and the previous data of 1 bit is stored in the RAM.
The data is input to the data control unit 501 from 502 .
The data control unit 50 uses the data one dot ago inputted from the RAM 502 and the data inputted now.
1, the address to be input to the ROM 503 is determined. The data is input as an address in the ROM 503, and information regarding the head drive time t is input so that the thermal head can be driven optimally.
It is read from the ROM 503. The read contents are output to the head driving time control section 504. The head drive time control section 504 controls the head drive circuit 505 for an optimum time based on the input data.The head drive circuit 505 drives the thermal head 506 for the controlled time, and
06 is supplied with power from a power source 507.

As is clear from the above embodiments, the present invention has the effect that an appropriate thermal head drive time can be obtained and an appropriate print density can be obtained using only the print information of one dot before and the print information of the dot to be printed now. There is.

[Brief explanation of drawings]

1A and 1B are diagrams showing the conventional thermal head drive timing and head temperature characteristics, FIG. 2 is a diagram showing the driving time according to the thermal head driving method of the present invention, and FIG. FIG. 4 is a diagram showing the head drive timing and head temperature characteristics. FIG. 4 is a diagram showing the thermal head drive timing and head temperature characteristics in another embodiment.
The figure is a block diagram showing a circuit configuration for realizing the thermal head driving method according to the present invention. 501...Data control unit, 502...RAM,
503...ROM, 504...head drive time control section, 505...head drive circuit, 506...thermal head.

Claims (1)

[Claims] 1. In a method of driving a thermal head that performs halftone density recording of n gradations by changing the head temperature stepwise from θ ₁ to _{θ o} , each n
A predetermined drive time t ₁ (Y) for each gradation print information, and a predetermined drive time t (m) for each n gradation print information to be printed now. A method of driving a thermal head in which the driving time is the sum of 2. In a method of driving a thermal head that performs halftone density recording of n gradations by changing the head temperature stepwise from θ ₁ to θ _o , each n
For each combination of gradation printing information and printing information of each n gradation to be printed now, a predetermined driving time t ₁ (Y) and printing of each n gradation to be printed now. A thermal head driving method in which the driving time is the sum of a driving time t(m) predetermined for each piece of information. (However, t(m)=t ₂ ′+t ₃ ′+…+t _n ′, t ₂ ′,
t ₃ ′,...t _n ′ are head temperatures θ ₁ →θ ₂ , θ ₂ →θ ₃ ,…θ
_n-1
→ is the head driving time necessary for the head temperature to rise to θ _n , and t ₁ (Y) is the head driving time necessary for the head temperature to rise to θ ₁ . )