JPS612570A - Trouble-detecting circuit for printing head driver - Google Patents

Abstract

PURPOSE:To enable accurate discriminative detection of a short circuit trouble in a plurality of printing head pin drives of a printer, by detecting a short circuit trouble, discriminatively from normal printing, on the basis of an output from the second comparing circuit which compares an output from the first comparing circuit connected to the second power source with the second reference value through a predetermined time constant circuit. CONSTITUTION:When a transistor 11 is turned ON due to the breakage, or short-circuiting, of some of transistors 11-1N, both voltages VA, VB at points A, B are raised in dependence on the first power source voltage Vcc1 to have waveforms similar to that of the voltage Vcc1. When resistances R1, R2, R3, R4 are so set that VB>VA at the time of such a short circuit, an output from the comparing circuit 12 is brought to a high level. In this case, a voltage Vcc2 has no relation to the voltages at the points A, B. By an output from the circuit 12, the voltage at a connecting point D of the time constant circuit R6, C1 is raised in accordance with the time constant through a resistor R5. The voltage VD at the point D is inputted to a negative terminal of a comparator 13 through a resistor R7, while a reference voltage VE is inputted to a positive terminal of the comparator, and a trouble is detected when VD>VE.

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Field of Industrial Application The present invention relates to a detection circuit for detecting short-circuit abnormalities in a plurality of print head pin drivers of a printer.

(2) Prior art and problems Conventionally, the print head pin driver (drive circuit) of a serial dot printer applies drive inputs 1 to N to the bases of drive transistors 11 to 1N whose emitters are grounded, as shown in the conventional circuit in Figure 2. , are connected to a first power supply VCcl from their respective collectors via drive coils L1 to LH.

The collectors of these transistors 11 to 1N are made common via a diode and connected to a point @ which is biased with a resistor r1 from the second power supply Vcc2, and this voltage ■ is input to the negative terminal of the comparator 2, and the second A reference voltage V6 is taken out from the voltage dividing point (3) of the resistor r2*r3 connected to the power supply Vcc2 of the comparator 2 and inputted to the positive terminal of the comparator 2. Connect the output of this comparator 2 from the second power supply Vcc2 to the 0 point biased with a resistor D4 Q1. This signal is passed through an AND circuit 3 together with the inverted signal of (input 1 to human power N) to set a clip-flop (FF) 4. and output it.

That is, when any of the print head pin drivers 11 to 1N is turned on, the output of the comparator 2 becomes high level, but
In the case of a short-circuit abnormality, the JAND circuit 5 outputs a high level even if inputs 1 to N are not applied, and sets FF4. This allows abnormalities to be detected.

However, the drawback of this circuit is that the comparator 2 is always on and the reference voltage vb is established, whereas the transistor 11
~1N is intermittent, so ■VcC1 and ■V in Figure 3
As shown by the timing of cc2, ■The rise of CC1 is performed after the establishment of Vcc2, and therefore the voltage level of the 0 point ■There is a period P in which α is less than the reference voltage Vb of the 0 point, so the 0 point voltage is at a high level Tonashi, it is considered abnormal even though it is not abnormal. As a countermeasure for this, Vcc
A method was adopted in which abnormality detection was disabled for a certain period of time after one injection. This time needs to be set long enough to take account of fluctuations and dispersions in the power supply, but it includes true abnormal times, and there is a risk of burning out the print head.

(3) Object of the Invention An object of the present invention is to provide a print head driver abnormality detection circuit that can accurately determine and detect short-circuit abnormalities in a plurality of print head pin drivers of a printer.

(4) Structure of the Invention In order to achieve the above object, the print head driver abnormality detection circuit of the present invention includes a detection circuit that is powered by a first power source and detects whether any of a plurality of print head pin drivers is turned on; a first comparison circuit that is powered by a power source and compares the output of the detection circuit with a first reference value corresponding to a short-circuit abnormality in one of the printing Radbin drivers; and a second comparison circuit that compares the output of the first comparison circuit with a second reference value through a predetermined time constant circuit, and uses the output of the second comparison circuit to determine and detect short-circuit abnormalities except for normal printing. It is characterized by this.

(5) Embodiment of the Invention The principle of the present invention is that in the conventional example shown in FIG.
The reason that and ■ are inverted during the P period is because ■ is the first power supply V
ccl, while ■ is dependent on the second power supply VcC.
This is due to the fact that it is established only by 2. Therefore, inputs VA and VB of comparator 2 are made to follow the rise of the first power supply, and a time constant is provided for the output of this comparator, and the time constant rises in the case of printing and in the case of short circuit abnormality. Since the stain pressures are different, a second comparator provided with a predetermined reference value is used to detect an abnormality.

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

In the figure, the collectors of the driving transistors 11 to 1N are connected in common through diodes, and connected to a first power supply Vcc1.
The base of the transistor 11 whose collector side is grounded is connected to the base of the transistor 11 whose collector side is supplied with power. The voltage (2) at the voltage dividing point (2) of the resistors R3+R4 of the collector circuit and the voltage Vn at the voltage dividing point (2) of the resistors R1+R2 separately branched from Vecl are taken out and input to the positive and negative terminals of the comparator 12, respectively.

The output of this comparator 12 is connected to the second power supply V via a resistor R5.
It is connected to the 0 point between the time constant circuit R6a connected to cc2, and further inputted to the positive terminal of another comparator 16 via a resistor R7. A reference voltage Vffi at a voltage dividing point 0 of resistors R8+R9 connected to the same power supply Vce2 is input to the negative terminal. Then, a flip-flop (FF) 4 is set by the output of the comparator 13.

In this configuration, if any of the transistors 1 to 1N is damaged or short-circuited and the transistor 11 is turned on, the voltages vA and Vn at points 2 and 2 both start up depending on the first power supply Vcc1, as shown in FIG. This is the relationship between the Vccl waveform. Conversely, resistors R1゜R2, so that VB > VA when short-circuited,
Set R3 and R4. As a result, the output of the comparator 12 becomes high level. At this time, ■ VC62 in the same figure is ■ point,
■Not involved in point voltage.

The output of this comparison circuit 12 is passed through a resistor R5 to increase the level at the connection point @ of the time constant circuit R6+C1 in accordance with the time constant. In this case, as shown in ■ in the same figure, VB v
The relationship between v and l VD is arranged in the same relationship from start-up, and there is no mutual inversion during the process.

By comparing the voltage VD at the 0 point through the resistor hole 7 and inputting the reference voltage VI+ to the positive terminal of the comparator 13, as shown in FIG. 5, Vo>Vm An abnormality is detected when .

On the other hand, in the case of normal printing, the rising stain pressure is ■! as shown in vr. It is set so that the voltage decreases before reaching L7 and does not exceed Vg. In this way, printing and short-circuit abnormalities can be distinguished.

(6) As described in detail, according to the present invention, when detecting a short-circuit abnormality in a plurality of print head drivers, the abnormality detection is disabled for a certain period of time after the first power source is turned on. It is possible to accurately distinguish and detect printing and short-circuit abnormalities without any problems.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the configuration of the embodiment of the present invention, FIG. 2 is an explanatory diagram of the configuration of the conventional example, FIG. 3 is an explanatory diagram of problems in the conventional example, and FIG.
Figure 5 is a diagram explaining the principle and operation of an embodiment of the present invention.A) In the figure, 11 to 1N are drive transistors, 4 is a flip-flop, 11 is a transistor, and 12 and 13 are comparators.

Claims (1)

[Claims] A detection circuit that is powered by a first power source and detects whether any of the plurality of print head pin drivers is turned on; and a detection circuit that is powered by the first power source and responds to a short-circuit abnormality between the output of the detection circuit and any of the print head pin drivers. a first comparison circuit that is connected to a second power supply and that compares the output of the first comparison circuit with a second reference value through a predetermined time constant circuit; A print head driver abnormality detection circuit, comprising: a comparison circuit, and detects short-circuit abnormality by excluding normal printing based on the output of the second comparison circuit.