JPS5814783A - Temperature control system for heat-sensitive recorder - Google Patents

Abstract

PURPOSE:To enable to obtain a dot pattern with uniform density, by a method wherein a heating resistance element of the same kind as that of heating resistance elements for recording provided on a heat-sensitive head of a heat-sensitive printer is additionally provided in proximity to the heating resistance elements for recording, and the temperature of the elements is detected at the time of passing an electric current for printing. CONSTITUTION:To detect the temperature at the current-passing time of the heating resistance elements Rh1-Rhn for recording which are selectively driven by a printing action, the heating resistanc element Rhz of the same kind as that of the elements Rh1-Rhn is additionally provided in proximity to the elements Rh1-Rhn on the thermal head 1. Each of the resistance elements Rh1-Rhn and Rhz has a positive or negative temperature coefficient, and when the resistance elements Rh1-Rhn are selectively driven by the printing action, the temperature of the head 1 is raised and the resistance values of the elements Rh1-Rhn and Rhz are changed. The change in the resistance value of the element Rhz is detected by a resistance-detecting circuit 4, and an output voltage of a voltage-controlling circuit 3 is controlled by the detection output. Accordingly, the elements Rh1-Rhn are provided with voltages corresponding to the temperature thereof, and are heated to a fixed temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in the temperature control method of a thermal recording device, which improves the accuracy of controlling the temperature of a heating resistor on a thermal head and makes it possible to record a dot pattern of uniform density. In particular, when energizing a recording heating resistor element that is selectively driven by a printing operation, the resistance value of the added heating resistor element or the resistance value of a recording heating resistor element that is not selectively driven during the printing operation is detected. Provided is a temperature control method that enables accurate temperature control by controlling the power supplied to a recording heating resistor element that is selectively driven by a detection output.

Thermal recording devices used in facsimiles, printers, etc.
A so-called thermal printer usually has a thermal head consisting of a plurality of heat generating resistive elements arranged in a vertical line, and while this head is in contact with the thermal paper surface, it is moved in the horizontal direction, that is, in the row direction, and the printing is performed. A dot pattern is recorded on the thermal paper by selectively heating heating resistive elements at positions corresponding to the pattern.

Note that there is also a type of thermal recording device that has a thermal head in which heating resistive elements are arranged corresponding to the dot positions of each horizontal line/line, and prints a dot pattern while moving the thermal paper. It is being In addition to thermal paper, there are also devices that use various types of thermal recording media. However, since the basic principle is the same, here we have a thermal head consisting of heat-generating resistive elements arranged in a single vertical row, which moves while in contact with the thermal paper for recording, and shoots dots onto the thermal paper. The case of printing a pattern will be explained.

In such thermal recording devices, the color density of the thermal paper changes depending on the ambient temperature of the thermal head, heat accumulation in the head due to electricity supply, etc., and density unevenness occurs especially when recording at high speed or high density. It has the disadvantage of being noticeable. Furthermore, the temperature of each heating resistor element of a thermal recording device changes depending on the usage conditions corresponding to the printing pattern, that is, the driving history, and takes various values during the printing operation. The problem was that there were limits.

In order to solve these problems and print dot patterns with uniform density, thermal recording devices have traditionally detected the temperature of the thermal head or the ambient temperature. Various methods have been proposed for controlling the power supplied to selectively driven heat-generating resistive elements of a thermal head so that the heat-generating resistive elements are operated at a predetermined temperature.

For example, one method for detecting the temperature of a thermal head is to use the fact that the resistance value of a heating resistor element changes in response to its heating temperature, and to control the temperature of the heating resistor element using the detected output of the resistance value. Are known.
.

In this method, when selectively driving the heating resistive element of the thermal head, the resistance value is measured each time immediately before starting energization. Then, the temperature of the thermal head is detected based on the measured value, and the drive current is controlled so that a predetermined heat generation temperature is obtained.

However, in this method, the temperature of the heating resistor element is detected when the current is not applied, so there is a limit to improving the temperature control accuracy. For example, a method of detecting the temperature of the head holder using a temperature sensor is also known.

According to this method, it is also possible to measure the heat generation temperature when the heat generating resistor element is energized, but the actual detected temperature is
For example, the temperature of the head holder itself, that is, the temperature of the heat-generating resistor element, is corrected in consideration of thermal conductivity and the like, so that it is not too difficult to detect indirectly. Therefore, even with this method, it is impossible to detect the entire actual temperature of the heat generating resistor element which melts when energized, and temperature control based on such measurement results is not necessarily accurate.

Therefore, the temperature control method of the present invention solves these inconveniences in conventional control methods, and makes it possible to detect the temperature of the heating resistor element for recording when the recording heating resistor element is selectively driven by the printing operation. The purpose is to improve control accuracy and obtain a dot pattern with uniform density.

To this end, in the temperature control system of the present invention, a heating resistor element similar to the recording heating resistor element is added close to the recording heating resistor element on the thermal head, and the recording heating element is selectively driven by the printing operation. When the resistance element is energized, the resistance value of the added heating resistance element or the resistance value of the recording heating resistance element that is not selectively driven during printing operation is detected, and the recording heating element is selectively driven according to the detected output. The power supplied to the heating resistor element is controlled.

FIG. 1 is a block diagram showing a configuration example of a head drive control circuit used when implementing the temperature control method of the present invention. In the drawing, / is a thermal head, Rh
, -Rhn is the heating resistive element for recording, Rh2 is the added heating resistive element, 2 is the drive circuit, 3 is the voltage control circuit, and Da is the resistance value horizontal circuit.

The circuit shown in FIG. 1 selectively drives the n recording heating resistive elements Rh, ~Rhn that constitute the thermal head/, using the corresponding drive input signals, and prints a dot pattern on thermal paper. , a recording heating resistor element Rh that is selectively driven.

The power supplied to ~Rhn is controlled by variably controlling the applied voltage in response to the detected heat generation temperature.

In addition, in order to detect the temperature of the selectively driven recording heating resistive elements when energized, the recording heating resistive elements Rh, ~Rhn, which are selectively driven, are placed in close proximity to the recording heating resistive elements Rh, ~Rhn, which are the same as these recording heating resistive elements. A heat generating resistive element Rh2 of the same type is added.

The recording heating resistive elements Rh, ~Rhn and the added heating resistive element Rh2 have positive or negative temperature coefficients, and the recording heating resistive elements Rh, ~Rhn
When is selectively driven, the temperature of the thermal head increases and the resistance values of these heating resistive elements Rh, -Rhn and Rhz change. The temperature of the thermal head increases significantly due to heat accumulation, especially when the recording speed or recording density is high.

Therefore, the resistance value detection circuit detects a change in the resistance value of the added heating resistor wire Rh2, and the output voltage of the voltage control circuit 3 is controlled based on the detected output.

Therefore, the recording heating resistor Rh that is selectively driven,
~Rhn is given an applied voltage corresponding to its temperature, and can be heated to a constant temperature.

As described above, in the temperature control method of the present invention, when the recording heating resistive elements Rh and ``-Rhn are energized by the printing operation, a change in the resistance value of the added heating resistive element Rh2 is detected, and the change is handled accordingly. Since the voltage applied to the recording heat-generating resistive elements Rh, ~Rhn, which are driven by the selection-day is controlled, the change in resistance value when not energized or the temperature of the head holder etc. when energized is controlled. Compared to a temperature control method that controls the supplied power in response to changes, it is possible to significantly improve the accuracy.

FIG. 1 is an example of a schematic diagram of head drive control (b) showing the specific configuration of FIG. 7. The symbols in the drawings are the same as in FIG. 1, and Trl to Tr n and TrB and T
+・1. is a transistor, ZD is a Zener diode,
D is a diode, Amp is an amplifier, vR is a variable resistor,
R1-R4 indicate resistors.

FIG. 3 is a block diagram showing another configuration example of a head drive control circuit used when implementing the temperature control method of the present invention. The reference numerals in the drawings are the same as those in FIG. 7, and the numerals on the left indicate the pulse width control circuit.

In the circuit shown in FIG. 3, the control 70- of the power supplied to the selectively driven recording heat generating resistive elements Rh, ~Rhn controls the energization in response to the change in the resistance value of the added heat generating resistive element Rhz. This differs from the previous figure 1 in that the time is changed.

In other words, the pulse width control circuit 2 stops outputting to the drive circuit 2 according to the detection output generated from the resistance value detection circuit 2 when the resistance value corresponds to a preset temperature, and selects the resistance value. Driven recording heating resistive elements Rh, -Rh
It operates so that the heat generation temperature of n is kept at a constant value.

The zp diagram is a block diagram showing still another example of the configuration of the head drive control circuit used when implementing the temperature control method of the present invention.

The symbols in the drawings are the same as those in FIGS. 1 and 3, and B indicates an analog switch circuit.

In the case of this FIG. 1I, the added heating resistor element Rh
2 is used for recording other than normal printing, such as underlining.

In order to detect the temperature of the heating resistor element during energization, all the heating resistors that are not selectively driven in the printing operation, among the added heating resistor element Rhz and the recording heating resistor elements Rh, ~Rhn, must be detected. Regarding the element,
Detect the resistance value.

The analog switch circuit 6 is provided for this purpose, and in this case, the resistance value detection circuit detects the average value of all the heating resistance elements that are not selectively driven.

The voltage control circuit 3 is controlled based on the average value of the detected resistance values, and the voltage applied to the selectively driven heat generating resistor elements is controlled.

Note that a pulse width control circuit 5 as shown in FIG. 3 is provided in place of the voltage control circuit 3, and a pulse width control circuit 5 as shown in FIG. It is also possible to variably control the energization time.

The following Fig. S is an example of a head drive control circuit showing a specific configuration of Fig. G. The reference numbers in the drawings are the same as in FIGS. 2 and 9, and the FETs, ~FETn and FET
ET2 is a field effect transistor, Tr21 to Tr2n and Tr2Z are transistors U.

~Un and U2 are inverters, R11~R1n and R,Z
, and RIIO'' R2n and R7z represent resistors.

This figure S shows in detail the circuit configuration corresponding to analog switch circuit B in figure G, and this part includes:
A circuit for correcting level fluctuations due to changes in the number of heating resistive elements that are not selectively driven is also added. Note that, in order to simplify the drawing, dotted lines and symbols indicating the analog switch circuits are omitted.

Field effect transistor FET, ~FETn and FETz
functions to select the heating resistive elements Rh, -Rhn and Rhz which are not selectively driven. That is, for a non-driven heating resistor element, the drive input signal is "01".
It is input at inverter U.

Since it is inverted by ~Un and Uz, the corresponding field effect transistors FET, ~FETn, and FET2 are made conductive, and the non-driven heating resistive element is connected in parallel to the resistance value detection circuit G.

1/3- Therefore, the output of the amplifier Amp of the resistance value detection circuit 3 becomes the average value of the resistance values of the non-driven heating resistor elements, and the voltage applied from the drive circuit 3 is controlled by the output signal of the voltage control circuit 3. Ru.

The transistors Tr2n and Tr2z and the resistor RtI=R2n are used to correct the level fluctuation of the amplifier Amp due to the difference in the number of heat generating resistor elements when not driven.

In the case of Figure 7 and the left figure above, the added heating resistor element Rhz is used for recording purposes other than normal printing, and the temperature detection when the heating resistor element is selectively driven by the printing operation is energized. In order to do this, the average value of all the resistance values of the non-driven heating resistance elements including the added heating resistance element is detected, and the applied voltage to the selectively driven heating resistance element is adjusted according to the change. The power supply is controlled by variable control of the energization time.

However, the added heating resistance element Rhz does not necessarily need to be used for recording, but is always used for -/dar temperature detection, and together with the non-driven heating resistance element for recording, it is used to detect changes in resistance value when energized. It is also possible to control the supplied power by detecting the average value.

Furthermore, even if the added heating resistor Rh2 is used for recording purposes other than normal printing, it is not necessarily necessary to detect the average resistance values of all non-driven heating resistors. do not have.

That is, changes in the resistance values of seven of the non-driven heating resistive elements including the added heating resistive element Rhz are detected, and the power supplied to the selectively driven heating resistive elements is controlled. Good too.

In this case, a multiplexer or the like is used instead of the analog switch circuit B in FIGS. 7 and S, and one of the non-driven heating resistance elements including the added heating resistance element Rh2 is selected. Make the resistance value detectable. In addition,
Priority is given to each heating resistor element in advance.

As explained in detail above, in the temperature control method of the present invention, firstly, in a thermal recording apparatus having a thermal head consisting of a plurality of recording heating resistive elements, the temperature control method is provided in a thermal recording device that is close to the recording heating resistive element on the thermal head. Then, a heating resistor element identical to this heating resistor element is added, and a means for detecting the resistance value of the added heating resistor element is provided. In accordance with the detection output from the detection means, the power supplied to the recording heat generating resistor element that is selectively driven is controlled.The power supply is controlled by keeping the energization time constant and adjusting the applied voltage. Alternatively, the applied voltage may be kept constant and the energization time may be varied.

First, in the temperature control method of such a thermal recording device, when the heating resistive element for recording which is selectively driven is energized, the resistance value of the added heating resistive element and the temperature which is selectively driven during the printing operation are determined. The resistance value of the recording heat generating resistor element which is not in use is detected, and the power supplied to the recording heat generating resistor element which is selectively driven is controlled in accordance with the detected output.

Finally, thirdly, in such a temperature control system, the added heating resistance element is used for recording purposes other than normal printing, and among the added heating resistance element and the heating heating resistance element for recording, printing The resistance value of all the heating resistance elements or one heating resistance element that is not selectively driven by the operation is detected, and the power supplied to the heating resistance element that is selectively driven is controlled according to the detected output. ing.

Therefore, according to the temperature control method of the thermal recording device of the present invention, it is possible to detect the change in temperature of the heating resistive elements for recording when the recording heating resistive elements are selectively driven by the printing operation and are energized. . The power supply is then controlled in response to the detected temperature.
The temperature control accuracy has been significantly improved, and a dot pattern with uniform density can be printed.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a configuration example of a head drive control circuit used when implementing the temperature control method of the present invention, and FIG. 2 is a head drive control circuit diagram showing a specific configuration of FIG. 1. For example, FIGS. 3 and 7 are block diagrams showing other configuration examples of the head drive control circuit used when implementing the temperature control method of the present invention, and FIG. 1 is an example of a head drive control circuit showing a typical configuration. In the drawing, / is a thermal head and Rh. ~Rhn is the heating resistance element for recording, Rh2 is the added heating resistance element, ko is the drive circuit, 3 is the voltage control circuit, da is the resistance value detection circuit, S is the pulse width control circuit, and ot is the analog switch circuit. show. -7g-

Claims (1)

[Scope of Claims] 1. In a thermal recording device having a thermal head consisting of a plurality of heating resistance elements for recording, a heating resistance element same as the heating resistance element for recording is located close to the heating resistance element for recording on the thermal head. and means for detecting the resistance value of the added heat generating resistor element, and when the recording heat generating resistor element selectively driven by the printing operation is energized, the detection output from the resistance value detecting means detects the selected value. A temperature control method for a thermal recording device characterized by controlling power supplied to a driven recording heating resistive element. 2. In the temperature control method of the thermal recording device according to claim 1 above, when the heating resistive element for recording is energized to be selectively driven, the resistance value of the added heating resistive element and the selectively driven resistor during the printing operation are controlled. 1. A temperature control method comprising: detecting a resistance value of a heating resistor for recording that is not being driven; and controlling power supplied to the selectively driven recording heating resistor based on the detected output. 8. In the temperature control method of the thermal recording device according to claim 1 above, the added heating resistor element is used for recording purposes other than normal printing, and the added heating resistor element and the recording heating resistor are used for recording purposes other than normal printing. Among the elements, the resistance values of all or seven heating resistance elements that are not selectively driven by the printing operation are detected, and the power supplied to the heating resistance elements that are selectively driven is controlled by the detection output. A temperature control method characterized by: 4. In the temperature control method for a thermal recording device according to claims 1 to 3 above, the power supplied to the recording heating resistor element is controlled by keeping the energization time constant and varying the applied voltage. A temperature control method characterized by: 5. In the temperature control method for a thermal recording device according to claims 1 to 3 above, the power supplied to the recording heating resistor element is controlled by keeping the applied voltage constant and varying the energization time. A temperature control method characterized by: