JPH01128851A - Applied voltage adjustor for thermal printing head - Google Patents

Abstract

PURPOSE:To enable adjustment with high accuracy, by connecting a dummy resistor to a common connection point of heat generating resistor elements, sequentially applying a predetermined voltage to the elements, calculating the average resistance of the elements on the basis of a voltage detected from a terminal for the dummy resistor, and adjusting an applied voltage for resistance heat generation on the basis of the average resistance. CONSTITUTION:An average resistance calculating circuit 24 outputs a mode switching signal SMC, a common connection point N of heat generating resistor elements is connected to a dummy resistor 20, and the circuit 24 instructs an applied voltage controlling circuit 12 to apply a voltage pulse for calculation of the average resistance of the elements to one of the elements, for example, the element R1. The voltage pulse is outputted from a terminal P1 of the circuit 12, whereby a voltage is generated across the dummy resistor 20, and is inputted to the circuit 24. On the basis of the voltage thus inputted, the resistance of the element R1 is calculated, and is stored into a buffer memory. Next, the circuit 12 is instructed to apply the voltage pulse to the element R2, and the resistance of the element R2 is thereby calculated. When the resistances of all of the elements are detected, the circuit 24 calculates the average of the resistances, and the circuit 12 adjusts an applied voltage for resistance heat generation. Thus, the need for troublesome manual adjustment is eliminated.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a head for a thermal line printer that records a visible image (image) on paper by generating heat from a heating resistor element, and particularly relates to a head for a thermal line printer that records a visible image (image) on paper by generating heat from a heating resistor element. The resistance value is determined and the applied voltage for resistance heating is automatically adjusted.

(Prior art) This type of thermal print head has a ceramic substrate as its main body, and a large number (for example, 1024) in a row on the substrate.
The heating resistor element is formed using thin film technology. These heat generating resistive elements are electrically connected in parallel and are selectively energized according to image information to record pixels with a density corresponding to the heat generated energy. This heating energy is determined by the level of the voltage applied to the heating resistor element or its pulse width.

(Problems to be Solved by the Invention) By the way, even with sophisticated thin film technology, variations in the resistance value of the heat generating resistor elements occur between the hemlocks. This variation causes variation in heat generation energy for a constant applied voltage, and therefore even the same type of heat generating head will perform different recording times.

Conventionally, in order to correct such variations, the applied voltage was adjusted using a volume control based on the average resistance value measured on the assembly line.

However, such adjustments are troublesome and troublesome, and place a heavy burden on line workers.

The present invention has been made in view of such problems, and provides an applied voltage adjustment device that automatically adjusts the applied voltage for resistive heating by determining the average resistance value of the heating resistive elements of a thermal print head. With the goal.

(Means for Solving the Problems) In order to achieve the above object, the present invention applies a voltage applied for resistive heating to a plurality of heating resistive elements arranged on a substrate of a thermal print head and electrically connected in parallel. a dummy resistor connecting means for connecting a dummy resistor to a common connection point of the plurality of heat generating resistors in order to determine the average resistance value of the plurality of heat generating resistors in the applied voltage regulator to be adjusted; a state in which the dummy resistor is connected; Means for sequentially applying a predetermined voltage to each of all or some of the heating resistor elements; Average resistance value determining means for calculating the average resistance value based on the voltages sequentially detected from the terminals of the dummy resistors; The structure includes voltage control means for controlling the applied voltage for the resistance heating based on the calculated value of the average resistance value.

(Function) When the dummy resistor connecting means operates and the dummy resistor is connected to the common connection point of the heat generating resistor elements, when a predetermined voltage is sequentially applied to each of all or some of the heat generating resistor elements. A current flows through the series circuit of the applied heating resistor and the dummy resistor, and a voltage equal to the resistance value multiplied by the current is generated between both terminals of the dummy resistor. The resistance value of the heating resistor element is determined from the detected voltage value.

In this way, each time the heating resistor element to which the voltage is applied changes, the voltage is sequentially detected from the terminal of the dummy resistor, and the resistance value of each heating resistor element is determined.

The average resistance value of the heating resistor element of the head is determined from all the resistance values thus obtained, and the applied voltage for resistive heating (for image recording) is adjusted based on this average resistance value. In other words, when the average resistance value is larger than the standard value, the applied voltage is lowered (when the average resistance value is smaller than the standard value, the applied voltage is increased, and the applied power (heating energy)
Adjustment is made so that the value becomes the standard value.

(Example) Hereinafter, one embodiment of the present invention will be described with reference to the accompanying drawings.

The figure shows the configuration of an applied voltage adjusting device according to this embodiment.

On the substrate of the thermal print head 10, a large number, for example, 1024 heating resistive elements R1 to RI024 are arranged in a row. These heating resistance elements R1-R102
4 are connected in parallel with each other, one terminal of each is connected to the voltage output terminals P1 to P 1024 of the applied voltage control circuit 12, and the other terminal is connected to each of the transistors 14 and 16 through a common connection point N. Connected to the collector.

The emitter of the transistor 14 is grounded, and the conductor is connected to the mode switching output terminal MC of the average resistance value determining circuit 24 via the inverting circuit 18. The emitter of the transistor 16 is connected to one terminal of the dummy resistor 20 and the input terminal of the A/D converter 22, and the base is connected to the mode switching output terminal MC of the average resistance value determining circuit 24.

The resistance value rd of the dummy resistor 20 is known, and the other terminal is grounded. Further, the output terminal of the A/D converter is connected to the data input terminal DI of the average resistance value determining circuit 24, and the data/control output terminal DC of the average resistance value determining circuit 24.
is connected to the data/control input terminal DC of the applied voltage control circuit 12.

Now, the voltage adjustment according to this embodiment is performed every time the power is turned on. First, the average resistance value determining circuit 24 outputs the mode switching signal SMC of logical value "H" from the mode switching output terminal MC.
Output. As a result, the transistor 16 is turned on, and the common connection point N and the heat generating resistor elements R1-R102 are turned on.
The other terminal of 4 is connected to the dummy resistor 20. On the other hand, the transistor 14 is off and in a cutoff state.

Next, the average resistance value determining circuit 24 calculates the applied voltage control circuit 1.
2, a control signal C8 is applied to instruct that a voltage pulse for determining the average resistance value should be applied to a specific heating resistance element, for example, R1.

Then, the voltage output terminal PI of the applied voltage control circuit 12
, a voltage pulse of, for example, 20 volts is output, which causes the heating resistive element R11 transistor 16. Current I+ flows to ground through dummy resistor 20, and dummy resistor 2
0 is the voltage V1 of the value obtained by multiplying the resistance value rd by the current II.
occurs.

This voltage Vl is converted into a digital value DV+ by the A/D converter 22 and input to the average resistance value determining circuit 24. The average resistance value determining circuit 24 uses this input data DVl.
The resistance value rl of the heating resistor element R1 is calculated based on the calculated value, and the calculated value is stored in the internal buffer memory, and then the voltage pulse for determining the average resistance value is sent to the applied voltage control circuit 12 to the heating resistor element R2. A control signal C8 is provided to indicate what should be applied.

Then, the voltage output terminal P2 of the applied voltage control circuit 12
A pulse of the same voltage (20 volts) as above is output from the heating resistor element R2, transistor 16. A current 2 flows to the ground through the dummy resistor 20, and a voltage v2 whose resistance value rd is multiplied by the current 2 is generated in the dummy resistor 20, resulting in a resistance value r of the heating resistor R2.
2 is calculated by the average resistance value determining circuit 24.

In this way, heating resistance elements R3, R4, R5 songs R+
For 024, the respective resistance values r3rLr5・
...i 1024 is calculated. Then, when the data (calculated values or measured values) of all the resistance values r l -r 1024 are collected, the average resistance value determining circuit 24 calculates (rl+r2
+...+r1024)/1024 is calculated to determine the average value r, and the data Dr is given to the applied voltage control circuit 12. The applied voltage control circuit 12 adjusts the applied voltage for resistance heating according to the average resistance value r■ of the heating resistance elements R1 to R1024. In other words, when the average resistance value r■ is larger than the standard value, the applied voltage is lowered, and when the average resistance value r■ is smaller than the standard value, the applied voltage is increased, so that the applied power (heating energy) is the standard value. Make adjustments so that

When the average resistance value measurement and voltage adjustment as described above are completed, the average resistance value determining circuit 24 connects the mode switching output terminal M
A mode switching signal SMC with a logical value of "L" is output from C. As a result, the transistor 16 is turned off, and the heat generating resistance elements R1 to R1024 and the dummy resistor 20 are cut off. On the other hand, the transistor 14 is turned on, and the common connection point N of the heating resistance elements R1 to R1024 is substantially connected to the ground. Under such conditions, each voltage output terminal P1 . P2. ...P
1024 selectively outputs a voltage pulse intended for resistance heating, that is, for image recording, and the current flowing through the heating resistance element flows through the transistor 14 to ground. Since the applied voltage of each voltage pulse is controlled by the above-mentioned voltage adjustment, the desired heat generation energy is applied from the heating resistor element to the ink film, and the desired one pixel according to the image information is recorded on the paper. be done.

In this way, in this embodiment, even if there is variation (error) in the average resistance value of the heating resistive elements R1 to R1024 of the thermal print head 10, the applied voltage is automatically adjusted to compensate for it. There is no need for workers to make cumbersome manual adjustments on the assembly line as in the past.

Further, since the voltage is adjusted every time the power is turned on, stable recording quality can be ensured even if the resistance values of the heating resistive elements R1 to R1024 change due to changes over time or the like.

In addition, in the above example, in order to obtain the average resistance value r■, the resistance values rl to r102 of all the heating resistance elements R1 to R1024 are used.
For example, R1, R5, R9, R13...
It is also possible to sample every fourth resistor, measure their resistance values r L r 5+ r L r 13- , and use those average resistance values as a substitute for the overall average resistance value.

(Effects of the Invention) As described above, according to the present invention, a predetermined voltage is sequentially applied to each of all or some of the heating resistance elements in a state where the dummy resistor is connected to the common connection point of the heating resistance elements. The average resistance value of the heating resistor element is calculated based on the voltage sequentially detected from the terminal of the dummy resistor, and the applied voltage for resistive heating (for image recording) is adjusted based on the warped average resistance value. This eliminates the need for the operator to perform troublesome manual adjustments, and allows for more reliable and highly accurate adjustments.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an applied voltage adjusting device according to an embodiment of the present invention. In the drawings: 10...Thermal print head, R1 to R+0
24... Heat generating resistor element, N... Connection point of the heat generating resistor element, 12... Applied voltage control circuit, 14.
...Transistor, 16...Transistor,
18... Inverting circuit, 20... Dummy resistor, 2
2... A/D converter, 24... Average resistance value determining circuit.

Claims (1)

[Scope of Claims] An applied voltage adjustment device that adjusts the applied voltage for resistive heating to a plurality of heating resistance elements disposed on a substrate of a thermal print head and electrically connected in parallel, comprising: dummy resistance connecting means for connecting a dummy resistor to a common connection point of the plurality of heat generating resistor elements in order to determine an average resistance value; means for applying a predetermined voltage; average resistance value determining means for calculating the average resistance value based on voltages sequentially detected from terminals of the dummy resistor; An applied voltage adjustment device for a thermal print head, comprising: voltage control means for controlling applied voltage for heat generation;