JPS62122370A - Thermal head - Google Patents

Abstract

PURPOSE:To set a thermal head to all the same initial conditions with respect to a test picture signal of a specific mode by resetting the contents of a shift register of electronic control systems in all semiconductor devices when a power source is energized. CONSTITUTION:The thermal head is checked under the condition when a printing direct current power source EB is set to a low voltage as low as possible and is set in such a manner that a large printing current does not flow to thermal printing resistance elements R1-R8 for a long period, respectively and the increase and the decrease in the current of the respective resistance elements can be easily detected by an ammeter 25. According to the processing, a burning accident of the thermal printing resistance elements when a bonding line of an enable signal input terminal contacts with an earth E can be previously prevented and the check for the completion in assembling the thermal head is carried out completely by an electric means. When the power source is energized together with the completion of setting of this state, the contents of the shift register 4 are al initialized from an unsteady state immediately before to '0' and a specific picture signal is inputted to a picture signal input terminal 22.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to thermal heads, and more particularly to the construction of semiconductor electronic circuits for driving thermally printed resistors.

(Prior Art) A thermal head is normally configured to simultaneously print a binary image signal sent from an image sensor device on the transmitting side line by line of a document.

For example, 1 m for Japanese Industrial Standards A row No. 4 manuscript paper.
Assuming that image signals are sent at a resolution of 8 pixels per image, the thermal head will have 1728 pixels for a paper width of 216m+*.
It is equipped with several thermal printing resistive elements, each of which is driven and controlled simultaneously by an electronic circuit inserted into each element. Therefore,
The 27 semiconductor devices that integrate these electronic circuits and the thermal printing resistive elements are interconnected by a large number of wire bonding lines, as many as 1,728 wires. In addition, each of the 27 semiconductor devices has a minimum of nine wire bonding lines, including a power supply terminal (including a ground terminal), a clock input terminal, an enable signal input terminal, an image signal input terminal, and others, so one thermal - The entire head actually includes a large number of wire bonding lines, exceeding 2,000, and an unreasonable number of connection points.

Generally, when a large number of wire bonding lines are used and the number of connection points increases dramatically, most defects in the assembly process occur at this bonding stage.

Therefore, upon completion of assembly, checks are mainly made on whether or not these connections are made correctly. For this check, a mounting test method is usually used in which a printing operation is performed using a test image signal.

(Problems to be Solved by the Invention) According to this mounting test method, the presence or absence and location of bonding defects can be easily found by visual inspection. However, if there is a failure in the control system of the electronic circuit that drives the thermal printing resistance element and the drive cannot be controlled, the thermal printing resistance element may be instantly burned out, so this is not necessarily the best means. In other words, when the electronic circuit is configured to gate drive the thermal printing resistor element with, for example, a "0" level enable signal, it is assumed that this signal input terminal is obscured and exposed to the ground. Then, at the same time as the power is turned on, the thermal printing resistor element connected to this electronic circuit is kept in a state of being driven, so that it is instantly blown out. Therefore, when checking the thermal head upon completion of assembly, it is desirable to take into account any failures in the electronic circuit control system and to be able to discover all bonding defects, including those on the semiconductor device side, without burning out the thermal printing resistor. .

[Purpose of the invention]

SUMMARY OF THE INVENTION In view of the above circumstances, an object of the present invention is to provide a method for completing assembly without burning out a thermal printing resistance element.

It is an object of the present invention to provide a thermal head equipped with an electronic control system capable of performing the following steps.

[Structure of the invention]

The thermal head of the present invention includes a semiconductor electronic circuit that sequentially stores and latches binary image signals in a shift register and gate-drives the thermal printing resistive elements all at once via an enable signal. The shift register of the electronic circuit is provided with reset circuit means for clearing the contents of the register upon power-on.

(Means for Solving the Problem) That is, according to the present invention, a reset circuit means is added to the shift register constituting one of the electronic control systems of the thermal head for clearing the contents of the register when the power is turned on. Ru.

(Function) As in the past, the shift registers integrated in multiple semiconductor devices are reset and reset at the same time as the power is turned on. Therefore, for example, the electronic circuits of 27 semiconductor devices respond to test image signals of a specific mode. Each thermal printing resistor element is driven and controlled under the same initial conditions, and different electrical modes are shown on the resistor element side in response to defects in the clock input terminal, enable signal input terminal, image signal input terminal, and other bonding lines. Therefore, it is possible to diagnose the quality of each semiconductor device individually. In addition, this diagnosis can be performed by electrical means instead of a printing test without passing a large current through the thermal head printing resistance element, so even if there is a failure in the electronic circuit control system, the thermal printing resistance element can be burnt out. I won't force you. The present invention will be described in detail below with reference to the drawings.

(Example) The figure is a circuit configuration diagram showing an embodiment of the present invention.

In this embodiment, in order to simplify the explanation, only the circuit configuration for 8 pixels is shown, and the thermal printing resistor elements 几, ~R6
The present invention includes a conventional part consisting of a printing resistor part l including a semiconductor device 2 having a drive control electronic circuit, and a newly provided part or an additional part of a set circuit device 3. Here, the semiconductor device 2 includes a shift register 4 that sequentially transfers and stores a binary image signal P using a clock CK, and latch circuits 5 to 12 that respectively latch the contents of this shift register 4.
Negation theory 3: This latch output is gate-controlled with enable signals E and ~E4, respectively! @product circuits 13 to 20,
The printing resistance element R, - which is opened to the open side by this gate output
R, and driving transistors Q, ~Q, and
The reset circuit device 3 includes a series circuit of a resistor R and a resistor C that pulls up the power supply voltage (VDI), and a reset circuit 21 that sends a reset signal φ to the shift register 4 when the power is turned on.
including. Further, terminals 22, 23 and 24 each receive a binary image signal P.

The assembled thermal head of the present invention is checked in this state by setting the DC power source E for printing to the lowest possible voltage. That is, thermal printing resistance elements R1 to R,
In order to prevent a large printing current from flowing for a long time, the ammeter 2
5, which is set to a level that can be easily detected. By this measure, it is possible to prevent the thermal printing resistor element from burning out when the bonding wire of the enable signal input terminal is in contact with the earth E. Therefore, the assembly completion check of the thermal head of the present invention is entirely performed by electrical means.

When the power is turned on with the completion of the above state settings, the contents of the shift register 4 are initialized from the previous indeterminate value to all O". Here, the image signal input terminal 22 receives a specific image signal "1, 0, 0°0...0" is input.

If there is no defective bonding between the black input terminal 23 and the image signal input terminal 22, the image signal "1" will be transferred to the next organ, and if there is no defective bonding with the thermal printing resistor element, the enable signals E, ~E4 will be transferred. With the input of , current sequentially flows from the printing DC power source EB to the thermal printing resistive elements EB, -. Therefore, if the ammeter 25 shows "O" when counting the numbers consisting of black and red CK,
This indicates that there is an abnormality in the semiconductor device including the electronic circuit of the corresponding control system.

That is, it can be presumed that this semiconductor device has a defective portion in any or all of the image signal input terminal 22, the clock input terminal 23, or the bonding wire with the thermal printing resistor element. Shift register 4 in exactly the same way
If there is a case where no change is recognized in the indication of the ammeter 25 when the signal "O" is shifted sequentially, the image signal input terminal 2 of the next semiconductor device is
2 has caused a contact accident with the power supply VDD.

The causes of failures in semiconductor devices have been described above with a focus on poor connection or contact of bonding wires, but even if the cause is in the semiconductor element itself that constitutes the electronic circuit, the various electrical aspects that appear on the ammeter 25 can be similarly explained. Due to the difference, a defective semiconductor device can be easily detected.

〔Effect of the invention〕

As described in detail above, in the thermal head of the present invention, the contents of the shift registers of the electronic control system in all semiconductor devices are reset when the power is turned on, and all test image signals in a specific mode are set to the same initial conditions. Therefore, a check at the time of completion of assembly can be carried out by a simple electrical means, and a defective semiconductor device can be easily detected without burning out the thermal printing resistor element as in the conventional case. That is,
Excellent effects can be achieved in terms of both reliability and productivity.

[Brief explanation of drawings]

The figure is a circuit configuration diagram showing an embodiment of the present invention. DESCRIPTION OF SYMBOLS 1...Printed resistance section, 2...Semiconductor device, 3...Reset circuit device, 4...Shift register, 5-12...・Latch circuit, 13
~20... NAND circuit, 21...
Reset circuit, 22... Image signal input terminal, 2
3-...Clock signal input terminal, 24...
...Power terminal, 25...Ammeter, VDD...
...Power supply potential, E...Earth, P...
211 [Image signal, E, ~E4...Enable signal, CK...Black signal, Qt~Q,...
・・・・Drive transistor, R0~⇠, ・・・Thermal printing resistor element, EB・・・・DC power supply for printing, φ・・・・Reset signal. Sara ゛Representative Patent Attorney Uchihara Toru. 11

Claims (1)

[Claims] A thermal printer comprising a semiconductor electronic circuit that sequentially stores and latches binary image signals in a shift register and gate-drives thermal printing resistance elements all at once via an enable signal.
A thermal head characterized in that the shift register of the semiconductor electronic circuit is provided with reset circuit means for clearing register contents upon power-on.