JPS5923672B2 - Temperature compensation method in halftone recording - Google Patents

Description

Detailed Description of the Invention This invention relates to a recording method that reproduces halftones by controlling the application time of a recording voltage. It is about the method.

Conventionally, recording techniques used in facsimiles and the like include discharge recording, electrostatic recording, heat-sensitive recording, and energization heat-sensitive recording. The methods for reproducing halftones in these recording technologies include a method in which the amplitude of the recording voltage is varied according to the image signal, and a method in which the application time of the recording voltage is varied in accordance with the image signal (hereinafter referred to as the pulse width control method). ). Among these methods, the pulse width control method is an effective means for discharge recording, thermosensitive recording, energization thermosensitive recording, etc. in which recording is performed by energization. This will be explained below using thermosensitive recording as an example. Figure 1 shows an image signal distribution circuit for reproducing halftones in thermal recording, in which 1 is a thermal head with a matrix configuration consisting of n blocks of heating resistors, each head having m pieces; is a driver on the side that selects within a block (x side), 3 is a driver on the side that selects a block (y side), 4a and 4b are m-bit tapped BBDs (bucket trigate devices), and 5 is a driver on the side that selects blocks (on the Y side). Reference signal generation circuit, 6a and 6b are comparators, □ is a channel switching circuit, 8 is a 1/m frequency dividing circuit, 9 is a clock distribution circuit, 10 is an n-bit shift register, C
LK, PIX, and PHS are terminals to which clock signals, image signals, and reset signals are applied, respectively.

The image signal is inputted from the terminal PIX, inputted to tapped BBDs 4a and 4b which perform read and hold operations alternately, and are exchanged in series and parallel.

The serial-to-parallel converted image signal is converted into a signal with a pulse width corresponding to the image signal by the reference signal generation circuit 5 and comparators 6a and 6b, and then sent to the thermal head 1 via the channel switching circuit T (driver 2 on the 5X side). Figure 2 shows how the serial-to-parallel converted image signal is converted into a pulse width. side input signal), 5
2 is a serial-parallel converted image signal (comparator 6 in Fig. 1).
one of the m bits of the input signal on one side of a, 6b),
S3 is the output signal of comparator 6a or 6b.

Here, T is the hold (
T=m/φ (φ is the frequency of the clock signal). Further, τ indicates the pulse width of the output signal S3 of the comparators 6a and 6b that changes depending on the image signal, and its variable range is 0≦τ≦T. By the way, in thermal recording, the ambient temperature is Tl, t2
, t3 (t1 x T2<T3), the recording density characteristics with respect to the pulse width (current application time) are characterized by a characteristic that the higher the ambient temperature is, the higher the recording density becomes, as shown in FIG.

For this reason, the conventional method has the disadvantage that the density of the recorded image tends to vary in level as a whole in response to changes in ambient temperature. In order to eliminate these drawbacks, this invention stabilizes the recording density with respect to the ambient temperature by lengthening or shortening the overall pulse width for the image signal according to changes in the ambient temperature. It is.

The present invention will be explained below with reference to the drawings. FIG. 4 shows an embodiment of the reference signal generation circuit according to the present invention.
11 is a monostable multivibrator, 12 is a bootstrap circuit, 13 is a thermistor, 14 is an adder, 15 is a comparator, and 16 is a distribution circuit.

In addition, R is a resistor, Tr is a transistor, C is a capacitor, VR is a variable resistor, ZD is a Zener diode, and C
P indicates a comparator. Here, S4 is 1/
This is the output signal of the m frequency divider circuit 8, and controls the timing of the sawtooth wave S5 generated in the bootstrap circuit 12. control Further, the adder 14 and the comparator 15 control the level of the reference signal S6, and the reference signal S6 slopes from the voltage e1 as shown in FIG. 5, and drops to a low level after reaching the voltage E2. Here, the voltages E, , e2 match the minimum and maximum values of the BBD output. Furthermore, the reference signal S6 is distributed at a predetermined timing by the distribution circuit 16 to become reference signals S7 and S8, which are sent to the comparator 6 shown in FIG.
a and 6b are supplied. By the way, the thermistor q-star 13 in the bootstrap circuit 12 controls the slope of the reference signal S5 with respect to changes in ambient temperature.

That is, when the ambient temperature is low, the resistance becomes large and the slope of the reference signal becomes gentle, and when the ambient temperature is high, the resistance becomes small and acts to increase the slope of the reference signal.

Therefore, as shown in FIG. 6, the reference signal when the ambient temperature is low is S9, and the image signal S output from the BBD is
2, the resulting signal has a longer pulse width like Sll. Conversely, when the ambient temperature is high, the reference signal becomes like SlO, and the pulse width for the image signal S2 becomes short like Sl2. In other words, the level of the image signal (
The characteristics of the output pulse widths of the comparators 6a and 6b with respect to the output of the BBD are shown in FIG.

In FIG. 7, voltage e1 represents the black level of the serial-parallel converted image signal, voltage E2 represents the white level of the image signal, and T4, t5, and t6 represent the ambient temperature.

As is clear from Figure 7, the pulse width changes overall as the ambient temperature changes, making it possible to compensate for the temperature dependence in the thermal recording shown in Figure 3. On the other hand, the density of the recorded image can be stabilized. Note that instead of the bootstrap circuit 12 shown in FIG. 4Q, a circuit in which a thermistor is inserted in series with the resistor that determines the slope may be applied in a triangular wave generation circuit using various types of integrating circuits such as a Miller integrating circuit. It is possible.

It goes without saying that the inclination in the above embodiments is not limited to a straight line as shown in the drawings, but may be, for example, a step-like one or a curved line such as an arc.

As described above, according to the present invention, it is possible to stabilize the density of a recorded image against changes in ambient temperature with a simple circuit configuration, and there are advantages such as improved reliability.

[Brief explanation of the drawing]

Figure 1 is an image signal distribution circuit diagram for reproducing halftones in thermal recording, Figure 2 is a waveform diagram showing how halftone information is converted to pulse width, and Figure 3 is pulse width in thermal recording. FIG. 4 is a diagram showing an embodiment of the reference signal generating circuit of the present invention, FIG. 5 is a waveform diagram of the reference signal in the present invention, and FIG. 6 explains the operation of the present invention. FIG. 7 is a characteristic diagram of the pulse width with respect to the level of the image signal in the present invention.

Claims (1)

[Scope of Claims] 1. A halftone recording method for reproducing halftones by applying a recording voltage having a pulse width corresponding to an image signal obtained by comparing an analog image signal and a reference signal to a recording medium, A temperature compensation method in halftone recording, characterized in that the slope of the reference signal is changed in accordance with the ambient temperature to compress or expand the pulse width of the recording voltage with respect to the image signal as a whole. 2. Temperature compensation in halftone recording according to claim 1, wherein the slope of the reference signal is controlled using the output of a bootstrap circuit formed by inserting a thermistor in series with a resistor. Method. 3. The temperature compensation method in halftone recording according to claim 1, characterized in that the slope of the reference signal is controlled by using the output of an integrating circuit formed by inserting a thermistor in series with a resistor. .