JPS62202764A - Printing head protective circuit for thermal printer - Google Patents

Abstract

PURPOSE:To enable a burnt state of each driver element in a printing head with a driver to be detected without taking off a signal line from an IC chip of each driver element, by comparing an output taken off on the downstream side of a serial resistor for a head power source with a threshold taken off on the upstream side of the resistor, and detecting a continuously flowing state of a current on the basis of a comparison output. CONSTITUTION:To reduce variations in printed density due to accumulation of heat, a serial resistor 3 and a parallel capacitor 4 are provided for a common head power source (f). A printing head protective circuit for preventing burning from occurring in a thermal head type printing head 2 with a driver mounted. The protective circuit comprises a means 22 for comparing an output 12 (b) taken off on the downstream side of the serial resistor 3 with a threshold 13 taken off on the upstream side of the resistor 3, and a means 21 for detecting a continuously flowing state of a current from an output 14 (c) from the comparing means 22, and an alarm signal 16 (e) is generated according to an output 14 (c) from the detecting means 21. For example, when the voltage on the downstream side of the resistor 3 is varied as indicated by (b) according to an operation of the printing head 2 and a current flows continuously due to a trouble at (g), the alarm signal 16 (e) is obtained as an output from a comparator 21 through the functions of the comparator 22 and an integrating circuit 18, 19.

Description

[Detailed Description of the Invention] [Summary] The present invention prevents burnout of a driver-mounted thermal dot print head by providing a series resistor and a parallel capacitor added to a common head power supply to prevent heat accumulation. In the print head protection circuit that operates, the output taken after the series resistor of the head power supply is compared with the threshold value taken from before the resistor, a state in which current continues to flow from the comparison output is detected, and an alarm is generated. occurs. As a result, it is possible to obtain a head protection circuit that is effective for this type of print head, which has been difficult to achieve in the past.

[Industrial application field]

The present invention relates to a head protection circuit that is effective for a thermal dot print head equipped with a driver.

[Conventional technology]

In conventional thermal print heads, a format in which the driver circuit is mounted on a carrier is often used. In this case, since the number of connector pins is large in order to transfer a plurality of parallel data corresponding to a plurality of printing elements, a method of parallel/serial conversion of data is adopted.

FIGS. 3(cL) and 3(b) are a schematic diagram (α) and a detailed diagram (b) of this type of print head.

In the same figure (α), in order to reduce the number of connector pins for print head 2 with driver, serial data ■, transfer (launch) timing signal @, and print timing are transferred to parallel/serial conversion circuit 1 into which parallel data is input. Only 3 signals of θ are transferred. On the other hand, the head power is supplied via a series resistor (C) 3 and a parallel capacitor (C) 4. This effect is due to the fact that when the head repeats a pattern with a large number of dots for a long time, the head's own heat is stored, that is, the temperature increases due to heat storage.

If heat accumulation is not taken into account, the head is initially cold, but near the end of printing, the density changes between the first print and the last print due to heat accumulation.

In order to prevent this heat accumulation, a resistor (R) 3 is connected in series to limit the current. However, if things continue as they are, the first print will be thin due to the current limit, and for this reason capacitor (C) 4
are connected in parallel, and the initial printing energy is secured by the charge stored in C. Such circuits are common and inexpensive, so they are often used.

FIG. 6 (6) shows a detailed view of the print head 2 with a driver.

That is, the shift register 11, latch circuit 12, and gate 13 are provided in parallel on the carrier. The serial data ■ from the parallel/serial conversion circuit 1 in the figure (α) is input and shifted to the shift register 11, latched to the latch circuit 12 by the transfer timing signal @, and this is input to the print timing signal θ.
The gate 13 is opened and the switch element 141~14%
Drive the pace of.

Head elements 15s to 15% connected in parallel from the head power source are connected to collector output circuits of these switch elements.

The ends of the collector output circuits of each switch element are short-circuited via diodes 161 to 16%, and the output ■ from the connection point is input to a transistor 170 pace provided with a base resistor γl and a bias resistor r2, and its output ■ is integrated by a series resistor 18 and a parallel capacitor 19, and the output ■
is compared with the voltage from the threshold power supply 20 by the comparator 21,
An alarm ■ is generated when a constant continuous signal is generated due to burnout.

FIG. 4 shows an operating waveform diagram in FIG. 3 (6).

That is, it is assumed that (α) in the figure shows a waveform (■) at the short-circuit connection point of the drivers 141 to 14%, and a constant continuation signal is generated at the 0 point.

On the other hand, (6) in the figure shows the collector output of the transistor 17, in which a continuation signal (2) corresponding to (2) is generated. In the figure (c), an output ■ which repeats a mountain-shaped waveform is formed by the integrating circuit in response to the output ■ in the figure (b), but the output of the comparator 21 is not output if it does not exceed the threshold value Vo. First, for ■, the output exceeds VO, and this generates an alarm as the output ■ in the same figure.

[Problem that the invention seeks to solve]

With the above configuration, in principle, burnout of each head element can be detected as an alarm, but since the print head with Draino is housed in the composite signal line Crab C chip of the output line of each driver element, it cannot be used as is. There was a problem that it could not be used and required a design change.

An object of the present invention is to provide a print head protection circuit that can detect the burnout state of each element without taking out the signal line from the IO chip of each driver element of a print head with Draino. [Means for Solving the Problems] To achieve the above object, according to the present invention, in a print head protection circuit for preventing burnout of a driver-mounted thermal dot type print head, a print head is provided after the series resistor of the head power source is removed. The output is compared with a threshold value taken from the front of the resistor, a state in which current continues to flow is detected from the comparison output, and an alarm is generated from this.

[For production]

With the above configuration, the state of burnout of each element of the driver element mounted on the print head is determined by Drino (the output taken out after the series resistor installed in the head power supply in the width 9 taken out from the element IC, and the output taken out from the front) Can be detected by comparing with the value.

Since this series resistor and parallel capacitor are provided externally apart from the print head, the current IO chip can be used without modification.

〔Example〕

FIG. 1 is an explanatory diagram of the configuration of an embodiment of the present invention.

In this figure, the difference from Figure 3 is that instead of extracting the change in print head operation from the short-circuit connection point of the driver element, it is extracted after the series resistor (R) 3 of the head power supply, and from before that, the change in the print head operation is extracted from the short-circuit connection point of the driver element. It is designed to extract and compare.

As a result, the protection circuit can be configured with only external circuits, regardless of the IO chip housing the driver element.

FIGS. 2(cL) to (e) are operational waveform diagrams of the embodiment of FIG. 1. The main part of the present invention shown in FIG. 1 will be explained below with reference to the waveforms shown in FIG. 2. That is, as the print head 2 operates, the current value from the head power supply ■ shown in Figure 2 (α) changes with υ, and the voltage ■ after the resistor (R) 3 changes to the value shown in Figure 2 (b). Assume that the current continues to flow due to a failure in (2). On the other hand, by setting the threshold value 0 from the voltage dividing point of the resistor rl + γ2 taken out from before the resistor (R) 3, and inputting it to the comparator (OOP) 22 together with the voltage @ for comparison, the result shown in FIG. (C) output 0 is obtained. The following configuration is similar to that in Figure 3, and the integration circuit (18, 1
9), the force output @ is set to a predetermined threshold value (Vo
) 20 into the comparator 21, and as its output the second
The alarm [stock] shown in figure (ε) is obtained. Waveform at the time of failure @
~[F] is also the same as in the case of FIG.

〔Effect of the invention〕

As explained above, according to the present invention, the output taken out after the series resistor (R) of the head power supply is set to the threshold value taken out before it, regardless of the IO chip housing the driver element of the print head. The burnout condition of the print head is detected by comparing it with the print head.

In this case, the series resistor (R) is externally attached together with the parallel capacitor (0) to reduce the shading of the print, so it is easy to remove and inexpensive, and it can be fully effective as a protection circuit. I can do it.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of the configuration of the embodiment of the present invention, FIG. 2 is an operational waveform diagram of the embodiment of the invention, FIGS. 3(cL) and (b) are explanatory diagrams of the configuration of the conventional example, and FIG. The operating waveform diagram of the conventional example is shown below.
In the figure, 2 is a print head with a driver, 3 is a series resistor, 4 is a parallel capacitor, 11 is a shift register, 12 is a latch, 13 is a gate, 141~14% is a switch element, 15
1 to 15% are head elements, 161 to 16% are diodes, 17 is a transistor, 18 is a resistor, 19 is a capacitor, 20 is a threshold power supply, and 21.22 is a comparator.

Claims (1)

[Scope of Claims] In a print head protection circuit for preventing burnout of a driver-mounted thermal dot print head in which a series resistor and a parallel capacitor are provided in a common head power supply in order to alleviate printing shading caused by heat accumulation, comprising means for comparing an output taken out after the series resistor of the head power supply with a threshold value taken out from before the resistor, and means for detecting a state in which current continues to flow from the output of the comparison means, A print head protection circuit for a thermal printer, characterized in that an alarm is generated from the output of a detection means.