JPH0339469B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for detecting the resistance value of each heating element of a thermal head used in a thermal recording device.

[Prior art]

The above-mentioned thermal head is usually configured with a plurality of heating elements corresponding to the number of pixels in the main scanning direction of the recording medium, and power according to image information is supplied to each of these heating elements separately. Therefore, the heating element generates heat. Therefore, in a heat-sensitive recording medium placed in sliding contact with the thermal head, the portion of the thermal head corresponding to the heat generating portion develops color, thereby reproducing an image corresponding to the image information.

By the way, in the above-mentioned thermal head, when each heating element is formed by a thick film heating element, the resistance value usually varies by 20 to 30%. Further, even when the heating element is formed of a thin film heating element, a variation in resistance value of 5 to 20% occurs.

As described above, it is unavoidable for thermal heads to have variations in the resistance value of each heating element, and this also causes the quality of recorded images to be poor, with unstable density. In other words, when the thermal head is driven at a constant voltage, the amount of heat generated by each heating element is proportional to [V ² /R] (where V: applied voltage value, R: resistance value of the heating element), and the thermal head Even when the head is driven at a constant current, the amount of heat generated by each heating element is proportional to [I ² · R] (I: applied voltage value, R: resistance value of the heating element). The amount of heat generated by the heating element, that is, the density of the recorded image, is directly affected by the resistance value R of the heating element itself, and if there are variations in the resistance value R, the above-mentioned recording There will also be variations in the density of the image.

Therefore, conventionally, the resistance value of each heating element is detected in advance and this value is appropriately stored in a storage circuit, and when recording is performed, the drive energy of each heating element is determined according to the stored resistance value. I was trying to control it. FIG. 1 shows this conventional resistance value detection method.

That is, in FIG. 1, H is the row of the heating elements, and C1 and C2 are each one of the heating element rows H.
The first and second common electrodes D, which alternately supply power to the stacked heating elements, are the common electrodes C1 and C2 in the same heating element row H, respectively.
This is a drive signal supply electrode placed between the two and whose conduction to ground is selected under the control of a thermal head drive circuit (not shown). In this method, the heating element is Current values are determined at any time by energizing each bit one by one, and each of these determined current values is converted into a resistance value and stored in the memory circuit.

[Problems with conventional technology]

However, when the resistance values of the heating elements are detected by this conventional method, the following problems occur.

That is, if the heating element that is currently energized is, for example, dot a shown in FIG. flows at the same time, and the current value determined above was inaccurate, such as (i+1') for the same dot a. Of course, even if the above-mentioned resistance value is calculated based on such a value, it is impossible to obtain effective information on the resistance value for the same dot a, and in the end, the control itself of the drive energy of each heating element described above cannot be obtained. It was considered meaningless.

[Purpose of the invention]

This invention accurately detects the resistance value of each heating element to enable effective control of the driving energy of the heating element described above, and furthermore, realizes high-quality image recording without density unevenness. The purpose is to provide a value detection method.

[Structure of the invention]

In the present invention, when current is simultaneously applied between any one of the drive signal supply electrodes described above and each common electrode, in other words, there are two groups of the same common electrodes as in the example shown in FIG. 1 above. Then, two adjacent electrodes are sandwiched between any one drive signal supply electrode and these two groups of common electrodes.
Focusing on the fact that the aforementioned leakage current does not occur when two heating elements are driven at the same time,
In response to the selection of the drive signal supply electrodes, that is, the selection of at least two heating elements whose resistance values are to be detected, power is sequentially and simultaneously supplied to each of the common electrodes, and at this time, the current flowing through these common electrodes is separately controlled. The resistance value of each heating element to be detected is determined based on the sampled current value.

〔Effect of the invention〕

In this way, according to the resistance value detection method according to the present invention, it is possible to determine the true resistance value of each heating element, which is not affected by the leakage current.
Of course, this makes the control of the driving energy of the heating element described above very significant, and the heat-sensitive recorded images obtained by implementing such control are also of very high quality without any density unevenness. Become something.

〔Example〕

FIG. 2 shows an embodiment of the method for detecting the resistance value of a thermal head heating element according to the present invention.

In this embodiment, like the thermal head shown in FIG. 1, each of the plurality of electrically connected heating elements is formed by a plurality of drive signal supply electrodes and two groups of common electrodes arranged alternately. This invention is applied to a thermal head that is sandwiched between the heat generating elements, and in FIG.
C1 and C2 represent the common electrodes of the two groups, and D represents the drive signal supply electrode.

Now, in this embodiment, as shown in FIG.
By simultaneously applying voltages of the same level to the two common electrodes C1 and C2 corresponding to each selection of the drive signal supply electrode D, the selected drive signal supply electrodes such as dots a and b are sandwiched between the two common electrodes C1 and C2. Then, two adjacent heating elements are energized at the same time, and the currents i ₁ and i ₂ flowing through these heating elements are collected separately to determine the resistance value of each heating element corresponding to the same dots a and b. That is, in the case of the example shown in Fig. 2, the value of the current i ₁ corresponds to the resistance value of the above dot b, and the value of the current i ₂ corresponds to the resistance value of the above dot a. Therefore, if the value of the voltage applied to the common electrodes C1 and C2 is E, then (resistance value of the heating element corresponding to dot a) = E/value of current i ₂ (corresponding to dot b) A desired resistance value can be obtained depending on the value of (resistance value of the heating element)=E/current _i1 .

When the resistance values of the heating elements corresponding to dots a and dot b have been detected in this way, the adjacent drive signal supply electrodes are selected, and the same resistance values as above are detected for the heating elements corresponding to dots c and dots d shown in the figure. Repeat the value detection operation.

According to such a resistance value detection method, it is possible to obtain accurate resistance value information that is not affected by leakage current as described above.

Note that in this example, the above current value (second
The collection method of i ₁ and i ₂ ) shown in the figure is arbitrary.
For example, an ammeter may be inserted into each of the common electrodes to directly detect the same current value, or an appropriate resistor may be inserted into each of these common electrodes and the same current value may be detected based on the voltage across the resistor. The current value may also be detected.

Further, in the same embodiment, the case where the resistance value detection method of the present invention is applied to a thermal head driven by a constant voltage is shown, but the present invention can be similarly applied to a thermal head driven by a constant current. . Of course, even in this case, the basic principle of the invention remains the same.

Finally, FIG. 3 shows an example of a heat-sensitive recording apparatus constructed by employing the method of the above embodiment.

That is, in FIG. 3, 1 is the above-mentioned thermal head, and 2 is a constant voltage circuit commonly connected to each heating element of the thermal head 1 via common electrodes C1 and C2. In this device, a switch circuit S is provided in series with each drive signal supply electrode of the thermal head 1 so that the loop between the constant voltage circuit 2 and each heating element can be opened and closed separately. Current flows through each heating element only after S is closed.
That is, in the case of this device, when the mode selectors 31 and 32 are respectively on the a side, the constant voltage circuit 2 → transistor switches TR1 and TR2
→ resistors r1 and r2 → mode selectors 31 and 32 → the heating element → the switch circuit S → ground, and the mode selector 3
When 1 and 32 are on the b side, constant voltage circuit 2 → transistor switch TR1 and
Current flows through a loop of TR2→mode selectors 31 and 32→the heating element→the switch circuit S→ground. In addition, these switch circuits S and transistor switches TR1, TR2
The opening and closing of the thermal head drive circuit 4 is controlled by the output of a thermal head drive circuit 4, which will be described later.

The switching mode of the mode selectors 31 and 32 is controlled by a sequence controller (not shown), and in this device, the mode selectors 31 and 32 are connected to the terminal a.
When the mode selectors 31 and 32 are switched to the terminal b side, the first operation mode is to detect and store the resistance values of each heating element and perform calculations based on these resistance values (described in detail later). When the mode is switched to 1, the thermal head 1 is actually driven in the second mode. Various operations in these modes are also comprehensively controlled by the sequence controller.

First, the first operation mode will be explained.

Now, suppose that the mode selectors 31 and 32 are switched to the terminal a side and the sequence controller (not shown) outputs an execution command for the first operation mode.
is the above transistor switch TR1 and TR
Both switch circuits 2 and 2 are turned on, and then the switch circuits S are operated to output a scanning signal SC that turns on and off the switch circuits S sequentially from the end at a constant timing. As a result, a current corresponding to the resistance value of each adjacent heating element across the drive signal supply electrode D of the thermal head 1 is applied to each resistor r.
1 and r2, and satisfies the resistance value detection conditions in the method of the embodiment described above. Then, the voltages across the resistors r1 and r2, which are proportional to these currents, are sequentially taken into the A/D converters 51 and 52, respectively.

The A/D converters 51 and 52 convert the values of the voltages across the resistors r1 and r2 to an appropriate timing signal (synchronized with the scanning timing of the scanning signal SC) applied from the sequence controller. It is a circuit that sequentially converts the data into, for example, a 16-step digital signal based on the data, and these converted digital signals (hereinafter referred to as resistance value data)
RD1 and RD2) are then applied to the storage circuit 6.

The memory circuit 6 is a memory constituted by, for example, a RAM (random access memory), and has a capacity corresponding to at least the number of heating elements of the thermal head 1. The storage circuit 6 sequentially stores the outputs of the A/D converters 51 and 52, that is, resistance value data RD1 and RD2, based on a write control signal applied from a sequence controller (not shown), and also stores the resistance value data RD1 and RD2. The stored resistance value data RD1 and RD are read based on the read control signal.
2 (this read resistance value data is collectively referred to as RD). In addition,
The write control signal is also a signal synchronized with the scanning timing of the scanning signal SC, and this scanning signal
When the entire on-off scan of the switch circuit S by the SC is completed, the total resistance value data RD1 and RD2 of the heating element is stored in the memory circuit 6. These resistance value data RD read out based on the readout control signal are then applied to the arithmetic circuit 7.

The arithmetic circuit 7 calculates a value of τ _i (in this example, a time value) such that [τ _i /R _i ] becomes a constant value, assuming that the value indicated by each of the resistance value data RD is Ri. This is a circuit that sequentially calculates , based on a calculation control signal (assumed to be synchronized with the generation timing of the readout control signal) applied from a sequence controller (not shown). This calculation can be done by preparing in advance a table with appropriate variations of the value τ _i in consideration of the above-mentioned resistance value variation range of the heating element _. This can be achieved relatively easily by selecting the value of τ _i closest to satisfying the above condition from among the values of τ _i in this table based on the value. That is, when the heating element is formed of, for example, a thick-film heating element, its resistance value (R _i ) varies by 20 to 30%, so the value of τ _i is also in the range of, for example, 0.5 to 1.2 msec. It is sufficient to prepare eight time values in 0.1 msec steps as the table above, and each time the resistance value data RD is added, the above _conditions [(τ _i /R _i ) = constant]
Select the value of τ _i that is closest to satisfying . The value of τ _i for each heating element calculated in this way is used as time data TD in the second operation mode of the device, that is, thermal head 1, which will be explained next.
It is taken into the thermal head drive circuit 4 when actually driving the head.

The second operation mode will be explained.

When the calculation in the calculation circuit 7 described above is completed, the sequence controller (not shown) switches the mode selectors 31 and 32 to the b terminal side, and sends a ready signal to the thermal head drive circuit 4 indicating that recording preparation is complete. do. This places the device in the second operating mode.

The thermal head drive circuit 4 becomes ready for printing by receiving the ready signal, and, in the case of a facsimile, for example, stands by in preparation for the arrival of image information VD transmitted from a receiving device (not shown). When the image information VD is input, the thermal head drive circuit 4 selects a heating element to generate heat from among the heating elements of the thermal head 1 based on the contents of the image information VD, and Applicable time data for each body
TD is selected from the time data TD calculated by the arithmetic circuit 7, and based on the selected time data TD, the drive signal DS for each of the selected heating elements (corresponding to the transistor switches TR1 and TR2) is determined. (also serves as on-off control). The drive signal thus formed
DS is sequentially applied to the switch circuits corresponding to the selected heating elements of the switch circuits S, and the switch circuits are connected to the drive signal DS.
Turns on only for the time corresponding to the relevant time data TD. This time data TD determines the resistance value of the heating element R _i
As mentioned above, it is configured by the time value τ _i such that [(τ _i /R _i ) = constant] for each heating element when the time value is τ _i ,
If the thermal head 1 is driven with such a drive signal DS, even if there is a variation in the resistance value of each heating element, this will be well absorbed, and each selected heating element will produce substantially equal resistance. amount of heat generation will be obtained.

This operation of the thermal head drive circuit 4 is as follows.
This process is repeated for each line of the incoming image information VD. Then, when the driving of the thermal head 1 described above for all lines of the same picture information VD is completed, the thermal head drive circuit 4 transfers the next picture information.
Waiting again for the arrival of VD.

By executing the second operation mode by the device, the heat-sensitive recording medium (not shown) disposed in sliding contact with the thermal head 1 develops color with uniform density in the portion of the thermal head 1 corresponding to the heat-generating portion. Therefore, images that effectively correspond to the image information can be reproduced with high quality.

The drive signal DS generated in the thermal head drive circuit 4 is normally a pulsed signal, and in this device, the pulse width of the pulse signal is determined in accordance with the above-mentioned time data TD.

Further, in the figure, the switch circuit S and the mode selectors 31 and 32 are shown as contact type switches for convenience of explanation, but any switch circuit having the above-described functions may be used. In practical use,
Non-contact type switches such as transistor switches are often used because they are small and have excellent responsiveness and reliability.

Furthermore, in this example, since the constant voltage circuit 2 is used to apply voltage at an equal level to each heating element as shown in the same figure, the calculated value τ _i of the arithmetic circuit 7 is also applied to the time data TD. and this data
The application time of the voltage is controlled based on TD so that the amount of _heat generated from each heating element becomes substantially equal. Further, in the thermal head drive circuit 4, drive signals are formed such that the pulse levels of the pulse signals as described above are determined based on this level data, and these drive signals are applied to the respective heating elements. The amount of heat generated from each heating element may be made substantially equal by applying the heat directly to the heating element. Of course, in this case, the constant voltage circuit 2 and the switch circuit S will be used only in the first operation mode described above, but based on the configuration shown in the figure, a simple change in the connection mode can be made. As a result, a thermal recording device having the same configuration can be realized. The same applies to current-driven devices.

By the way, although this device was constructed assuming a normal binary recording type, it is also easy to develop the same device into a multi-gradation recording type device that can also reproduce halftones. . That is, in this case, the calculation circuit 7 calculates the calculated value τ _i
By repeating subtraction or division based on , a number of pieces of data corresponding to the number of recording gradations are prepared for each heating element. At the same time, for each selected heating element, data corresponding to the density content (gradation content) of the image information is selected from among the data prepared by the arithmetic circuit 7, and these selected data are Based on this, a drive signal for each of the selected heating elements may be generated. These data can be converted into time data depending on the driving method of the thermal head.
Alternatively, it may be used as level data, as in the previous example.

Only when the resistance value of each heating element can be accurately detected as in the present invention, the realization of such a multi-gradation recording type thermal recording device becomes meaningful.

[Brief explanation of drawings]

FIG. 1 is a partial schematic diagram of a thermal head showing a conventional method for detecting the resistance value of a thermal head heating element, and FIG. 2 is a partial schematic diagram of the same thermal head showing an embodiment of the method for detecting the resistance value of a thermal head heating element according to the present invention. FIG. 3 is a block diagram showing an example of a thermal recording apparatus constructed by employing the embodiment method shown in FIG. 2. H... Heating element row, C1, C2... Common electrode, D
...Drive signal supply electrode, S...Switch circuit, r
1, r2...Resistor, 1...Thermal head, 2
... Constant voltage circuit, 31, 32 ... Mode selector, 4 ... Thermal head drive circuit, 51, 52
...A/D converter, 6...memory circuit, 7...arithmetic circuit.

Claims (1)

[Claims] 1. A plurality of drive electrodes Di and Di+1 each independently driven by an image signal are arranged on a linear heating element H formed continuously, and two groups of drive electrodes are arranged between the plurality of drive electrodes. In a method for detecting the resistance value of a thermal head heating element which is divided into heating elements Hi corresponding to recording dots by alternately arranging common electrodes C1 and C2 of the plurality of driving electrodes, the method comprises driving any one of the plurality of driving electrodes. electrode
Di is selected, and current is simultaneously applied between the selected drive electrode and the two groups of common electrodes C1 and C2. A method for detecting a resistance value of a thermal head heating element, characterized in that the resistance values of two heating elements Hi and Hi+1 adjacent on both sides of the selected drive electrode are determined based on the values i1 and i2.